DE2549181B2 - METHOD FOR MANUFACTURING A PHOTOLOCULATIVE POWDER - Google Patents

Description

45

5 °

The invention relates to a method for producing a photoconductive powder in which CdS, CdSe, If necessary, a flux is added to CdSSe or ZnSe, and the mixture is heated, washed and dried will.

In known methods for producing a photoconductive powder, a mixture of a cadmium sulfide-like material, an activator such as copper or silver, for the formation of electron acceptor sites in the material concerned, a donor material, e.g. B. a halide, for formation from donor sites and a flux such as cadmium chloride, sodium chloride and zinc chloride to temperatures heated above the melting point of the flux to control atomic valence. Photoconductive Powders of various properties were obtained by changing the proportions of the various Components and / or the heating temperature.

A disadvantage of such known methods, however, is that it causes very great difficulties, the To control photoconductor properties of the respective product. This is due to the fact that the Reaction products very sensitive to changes in the amounts of activator and donor material as well react to their relationship with one another. In addition, the dark resistance of the respective product is low and / or its "memory effect" is great, even if the respective product is compatible with the others desirable properties. Furthermore, the known methods still have the disadvantage afflicted that the powder obtained in the course of heating to form coarser particles Caking tends to occur. So when the photoconductive powder produced by such a method for Image formation in the electrophotographic field, in image conversion or in image enhancement, is used, you only get a low resolution image because the surfaces of the formed photosensitive materials are not even and smooth.

In order to meet the difficulties outlined, for example, a method for producing a photoconductive cadmium sulfide powder has already been developed in which silver or copper as an activator, a halide as a donor and an alkali metal or alkaline earth metal sulfate in an amount of 0.05 to 1.5 parts (e) cadmium sulfide per 100 parts are used as a dispersant and ^{heated to a temperature in the range from 400 to 600 °} C. (cf. DT-OS 22 00 061). However, the photoconductive powder obtained by this method has a relatively coarse particle size, on the order of several microns. Furthermore, the dark resistance and the "memory effect" of the photoconductive powder obtained in this way are inadequate. In fact, a practical cadmium sulfide type photoconductive material which is practically satisfactory as an image forming material particularly in binder-containing electrophotographic recording materials in which the photoconductive particles are dispersed in a resinous binder has not yet been produced.

The invention was based on the object of not having the disadvantages of the known photoconductive powder attached photosensitive powder excellent photoconductivity and very produce small particle size.

The subject matter of the invention is thus a method of the type described at the outset, which is characterized is that an activator-free CdS, CdSe, CdSSe or ZnSe with a dispersant and optionally mixed with an inorganic electron donor, heated, washed, dried and then im Heated again under vacuum, in a stream of nitrogen or in the presence of sulfur or hydrogen sulfide will.

When carrying out the process according to the invention, a very small particle size is obtained exhibiting and extremely light-sensitive, cadmium sulfide-like phosphorus powder.

The dispersant is expediently used after the process according to the invention has been carried out washed out with water.

Since in the context of the method according to the invention in the production of the cadmium sulfide-like photo

. If there is no activator present, the ^{process according to the invention is very simple; in addition, the photoconductor powder} obtained according to the invention can be used particularly well as a light-sensitive due to its very small size. ^el ji · Vm photoconductive material in the photosensitive u -hten of electrophotographic Aufzeich- ^S ^ materials in which the photoconductor powder T is hmäßig dispersed using. With the help of her electrophotographic Aufzeichnungsmate- ■ r η ι receives one copy images excellent dissolution t high contrast and - if at all Ätens slight veil. In addition, Figure 5 shows _as erffndungsgemäß producible photoconductor powder ^ entertaining electrophotographic recording Ä only a very small dark decay. Sm the process of the Erfmdung ~ L> ndbaren according cadmium sulfide-like materials are commercially available as ^V photoconductive powder. This is for example cadmium sulfide, cadmium selenide, cadmium sulfide selenide or zinc selenide

^m Suitable electron donors are halides, such as ammonium chloride or '"-" - "'.-" - ^ "" _D .. _t, _

10

, ₅

₂ o

Metals ζ B of aluminum, gallium or indium. ₂₅ ffipr

Fluxes that can be used are agents that _{melt at the heating temperature} maintained at J0 and melt the cadmium sulfide-like material. These are, for example, halides such as cadmium chloride, zinc chloride, sodium chloride or potassium chloride. . . 3

The dispersants which can be used according to the invention either do not melt as such or the cadmium sulfide-like materials do not melt at the temperatures prevailing during heating. Melt the maintained temperatures or not. They can be used both as fluxes and as dispersants. That is, if the heating temperature is below the melting point of the material in question, it can be used as a dispersing agent. However, if the Erh.tzungsr _e mperature is above the melting point of the material in question ^, it serves as a flux. So S bef _P ielsweis _e ^g sodium chloride behaves as midstream, at temperatures above 800 ° C, since it at 800 C Slzt. Conversely, the sodium chloride can be used as a dispersant if the temperature is below the melting point.

The dispersants used according to the invention have an excellent effect on the p-shaped fired cadmium sulfide-like material particles do not stick to each other when melted stick so that (thereby) the formation of a very fine photoconductive powder of high light-sensitive

The weight of the photosensitive powder obtained according to the invention depends somewhat on the particle size of the particular cadmium sulfide-like Iu material, the amount, type and particle size of the dispersant used and the state of suspension. In particular, however, the type and grade of the dispersant exerts a relatively large influence on the particle size of the photoconductive powder.

The amount of dispersant added should expediently be 20% by weight or more, more preferably be more than 50% by weight of the cadmium sulfide-like material used. The bigger the crowd of dispersant compared to the amount of cadmium sulfide-like material used, the the photoconductive powder formed becomes finer.

The dispersants which can be used according to the invention should preferably have a high purity, do not chemically react with the cadmium sulfide-like materials when heated, a melting point have above the melting point of the flux used, at the heating temperatures of the Materials do not melt and be water soluble.

If in the context of the method according to the invention, for example, cadmium chloride is used as a flux is used, sodium chloride, potassium chloride, sodium bromide, potassium bromide, Sodium iodide, potassium iodide, cadmium sulfate, zinc sulfate, sodium sulfate, potassium sulfate and the like be used. These substances melt at temperatures above the melting point of cadmium chloride and provide uniformity when using dispersion media such as water and alcohol Dispersions. Furthermore, since they are water-soluble, they can be easily removed by simply soaking them after Heat to be washed out. These dispersants most conveniently promote one easy production of the desired photoconductive powder.

According to the invention, water or any desired organic solvent, such as Alcohol, acetone, methyl ethyl ketone and ethyl acetate, preferably water or a water-soluble organic solvent such as methanol, ethanol, propanol or acetone can be used.

It is known to those skilled in the art that controlling the atomic valence of the cadmium sulfide-like materials the addition of an activator increases the dark resistance and sensitivity of the product. It has, however shown that when using the fine powder obtained according to the invention with increasing amount of Activator, although the sensitivity increases, the dark strength does not always increase, in fact it does can decrease. In contrast, have the invention by heating in the absence of Activators and finely divided photoconductive powders obtainable in the presence of dispersants are not only the same sensitivity (as can be achieved with the addition of activators), but also a higher sensitivity Dark strength and thus a higher initial stress which leads to the formation of high-contrast images, as well as a lower »memory effect«. Consequently the photoconductive powders obtainable according to the invention are outstandingly suitable for use in the case of electrophotographic transfer

^a The theoretical mechanism of the effects that can be achieved according to the invention has not yet been fully clarified, but it is presumably based on the following facts

th:

1. Using dispersants of the type described in accordance with the present invention gives very good results fine particles with an excellent crystal structure. This increases the number of particles per

Unit of volume of the light-sensitive layers, which results in a high level of dark resistance.

2. Non-activated metals (components of the activators) near the particle surface after Heating in the presence of activators adsorb water and the like, thereby reducing the Darkness is lowered.

3. It is known that cadmium vacancies are formed in cadmium sulfide-like crystal systems during heating form. Furthermore, it is known that the area of the as a result of exposure to light such crystals emitted photoelectrons larger than the area of the emitted photoelectrons when activated crystals are exposed to light. These cadmium vacancies can of course depending on their »number to increase the sensitivity just as much! or more how (than) the activators, like silver and copper, contribute.

20th

According to the invention, the heating can be carried out in the absence of fluxes and / or electron donors if the dispersant consists of a halide, for example (this reacts then part of the halide with the cadmium sulfide-like starting material used and can in this shape actually act as a flux during heating) and / or when part of the Halide also behaves as a donor in the course of the mixing process during heating. if for example, sodium chloride as a dispersant without the addition of any fluxes or electron donors Cadmium sulfide is added (see. Experiments 2 and 7 below in Example 1), the following runs Reaction from:

CdS + 2 NaCl-CdCl ₂ -I-Na ₂ S

Presumably the reaction product cadmium chloride acts as a flux or electron donor when heated and the sodium sulfide as well as the sodium chloride as a dispersant.

The conditions for the first heating in the context of the production of the cadmium sulfide-type photoconductive powder according to the invention depend on the respective cadmium sulfide starting material, electron donor, flux and dispersant as well as the desired particle size, the desired properties and the end use of the particular photoconductive powder to be produced. The first heating is preferably carried out by adding a mixture of 0 to 10 parts by weight of electron donor, 0 to 100 parts by weight of flux and 20 or more parts by weight of a dispersant, for example pulverized in a ball mill and then sufficiently dried on an evaporation device, which is sufficient for dispersion, in each case per 100 parts by weight cadmium sulfide-like material, and a suitable amount of the dispersion medium in a quartz tube and the whole is then heated ^{in air to a temperature of 400 to 800 0 C in a temperature-controlled electric heating furnace.} The product obtained during the first heating is then washed thoroughly with water and dried to remove the dispersant and the other water-soluble salts. The second or final heating can be carried out in such a way that the washed and dried product is transferred to a quartz tube and heated ^{to a temperature of 350 to 700 ° C. in a vacuum or in a stream of nitrogen and in the presence of sulfur or hydrogen sulfide.}

The following examples are intended to illustrate the process according to the invention in more detail.

example 1

High purity cadmium sulfide or cadmium sulfide selenide with a particle size of 0.05 to 0.5 microns (cadmium sulfide-like starting material) was fluxed with cadmium chloride or potassium iodide, Ammonium chloride as an electron donor, sodium chloride, sodium sulfate or cadmium sulfate as a dispersant and pure water or absolute ethanol as a dispersion medium (for the comparison samples also added copper (II) chloride as an activator)

The amounts of the various ingredients are given in Table 1. The mixture obtained in each case was mixed and pulverized for 6 hours in a stirred ball mill and then ^{dried for about 10 hours at a temperature of 140 °} C. in an aluminum trioxide crucible. The dry mixture in each case was transferred to an electric furnace and heated to a temperature therein for 1 hour heated from 500 to 700 ° C (first heating). After the completion of this heating, the heated material was cooled to room temperature, then poured into pure water, washed by decantation and dried. The washing with water was completed by decanting about 20 times until no more chloride ions were detectable in the washing water. The product obtained consisted of a crystalline, finely divided powder and was photoconductive. In order to increase the dark resistance and photoconductivity, this product has now been subjected to the following treatment.

About 0.5% high purity sulfur powder was added to the product and the mixture was thoroughly stirred. After stirring, the mixture was filled in a quartz tube for 20 minutes was heated in a nitrogen atmosphere to a temperature of about 500 ° C (second heating), then atmosphere in a nitrogen cooled to a temperature of 200 ⁰ C and finally dried in a desiccator.

The particle size distribution of the various products (of experiments No. 1 to 4 and 6 to 14) and Comparative experiments (experiments Nos. 15 to 20) were determined using a scanning electron microscope The results obtained here are contained in Tables I and II below.

Example 2

A mixture of 80 g of high purity cadmium selenide with a particle size of 0.5 to 1 micron (cadmium sulfide-like Starting material), 14 g of cadmium chloride as a flux and 1.8 g of ammonium chloride as an electron donor in 40 ml of pure water was ground and mixed for 6 h in a stirred ball mill and then dried on an evaporator at a temperature of 140 ° C for about 15 hours The dry mixture obtained was with 170 g of sodium chloride as a dispersant and 115 ml of absolute Ethanol was added as a dispersion medium, whereupon the mixture obtained was again stirred for 6 hours

Grind the ball mill and shape it into a uniform shape and then place it on an evaporator for about 10 hours was dried at a temperature of 120 ° C. The dry mixture was applied to the Crush the size of millet seeds, put them in a quartz tube and place in an electric oven for 15 minutes heated to a temperature of 590 ° C in air. After cooling to room temperature, the heated one Product washed thoroughly with pure water in the manner described in Example 1 and then dried.

The dry product was then transferred to a quartz glass tube, then in hydrogen sulfide for 10 minutes atmosphere to a temperature of 500 ° C and finally for 10 minutes in a vacuum to a temperature heated from 500 ° C. The heated product was cooled to a temperature of 100 ° C. in vacuo and then dried in a desiccator.

The particle size distribution of the product obtained (Experiment No. 5) was determined. The results obtained in this way are also shown in Tables 1 and II contain-.

Table 1

Ver
search
No. Starting
material
(50 g) Flux
(G) Activator
solution with
ΙΟ- ⁴ mol / ml
(ml) Electron
donator
material
(G) Dispersing
middle
(G) Dispersions
medium
(ml) Heating
temperature (° C)
1st stage 2nd stage 500 1 CdS CdCh - 5/2 H2O
4th - NH4CI
0.5 NaCl
150 H2O
80 580 500 2 CdS - - - NaCl
150 H2O
80 580 500 3 CdS Kl
4th - - CdSO4
150 H2O
80 700 500 4th CdS CdCb · 5/2 H2O
10 - NH4CI
2.0 NaCl
150 H2O
80 580 500 5 CdSe CdCb · 5/2 H2O
14th - NH4CI
1.8 NaCl
170 C2H5OH
115 590 500 6th CdSSe CdCb · 5/2 H2O
10 - NH4CI
5.0 NaCl
100 H2O
80 580 500 7th CdS - - - NaCl
250 C2H5OH
80 ' 580 500 8th CdS CdCU · 5/2 H2O
4th - NH4CI
0.5 NaCl
50 H2O
40 580 500 9 CdS CdCb · 5/2 H2O
4th - NH4CI
0.5 NaCl
250 H2O
120 580 500 10 CdS CdCb ■ 5/2 H2O
4th - NH4CI
0.5 NaCl
1000 H2O
400 580 500 11th CdS - - - NaCl
150 H2O
80 650 400 12th CdS - - - NaCl
250 H2O
80 700 450 13th CdS - - - Na2SO4
200 C2H5OH
80 600 45C 14th CdS - - - NaCl
200 H2O
80 500 50 ( 15th CdS CdCb · 5/2 H2O
4th CuCb
0.05 NH4CI
0.5 NaCl
150 H2O
80 580 50 < 16 CdS CdCb · 5/2 H2O
4th CuCl ₂
5.00 NH4CI
0.5 NaCl
150 H2O
80 580 50 ' 17th CdS - CuCb
5.00 - NaCl
150 C2H5OH
80 580 50 18th CdS CdCb · 5/2 H2O
4th - NH4CI
0.5 - H2O
80 580 50 19th CdS CdCb · 5/2 H2O
4th CuCb
0.50 NH4CI
0.5 - H2O
80 580 5C 20th CdS CdCb ■ 5/2 H2O
15th CuCb
5.00 NH4CI
2.0 - H2O
80 580

Il 9 Particle size (μ) 0.5-1 1-2 25th 49 181 L. 10-20 I) 30-40 40- 0-0.5 of the particles r ⁷ 10 Tabel Number ι 53 18th _ Vcr-
search 24 63 2 No. 33 43 21 2-5 5-10 20-30 28 46 26th 1 11th 18th 76 5 _ 2 - 4th 82 2 - - 3 2 68 16 8th - - 4th 12th 18th 38 17th - _ _ 5 4th 58 9 6th _ _ 6th 33 43 - 12th - _ 7th 57 54 4th 4th - _ _ 8th 41 63 20th 30th 10 _ _ 9 14th 68 10 - - _ 10 21 43 10 - - _ 11th 47 47 30th 1 - 12th 22nd 46 32 3 - _ 13th 18th 63 22nd 1 14th 7th 3 10 _ _ 28 5 _ 15th - - - 1 29 10 2 16 - - - 4th - 40 11th 17th - 8th _ 18th 12th 33 19th 19th 8th 28 23 20th - 24 25th

The results shown in Table 11 show that yeast can be controlled. In addition

In the experiments according to the invention through 30, the excellent crystal structure of the inven

X-ray heating in the presence of the specified dispersants

tel and confirmed diffraction obtained in the absence of activators.

Products have a small particle size of about 1 In contrast, those in the presence of voi

Micron diameter and that their partial activators or in the absence of dispersants!

Chen size distribution by changing the proportions 35 heated comparison products of usually large

on the cadmium sulfide-like starting material used, average particle size of 10-20 microns. material, electron donor, flux and dispersant

Claims (8)

Patent claims: 1. A method for producing a photoconductive powder in which CdS, CdSe, CdSSe or ZnSe if necessary, mixed with a flux, the mixture is heated, washed and dried, characterized in that an activator-free CdS, CdSe, CdSSe or ZnSe with a Dispersant and optionally mixed with an ι ο inorganic electron donor, heated, washed, dried and then in vacuo, in a stream of nitrogen or in the presence of sulfur or hydrogen sulfide is heated again. 2. The method according to claim 1, characterized in that that as dispersants sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide. Potassium iodide, cadmium sulfate, zinc sulfate, sodium sulfate or potassium sulfate is used. 3. The method according to claim 2, characterized in that that at least 20 parts by weight of dispersant per 100 parts by weight of CdS, CdSe, CdSSe or ZnSe can be used. 4. The method according to claim 1, characterized in that ammonium chloride is used as the electron donor or an aluminum, indium or gallium compound is used. 5. The method according to claim 4, characterized in that 0 to 100 parts by weight of electron donor can be used per 100 parts by weight of CdS, CdSe, CdSSe or ZnSe. 6. The method according to claim 1, characterized in that cadmium chloride as the flux, Zinc chloride, sodium chloride or potassium chloride is used. 7. The method according to claim 1, characterized in that the heated CdS, CdSe, CdSSe or ZnSe is washed with water. 8. The method according to claim 1, characterized in that the dispersant and optionally electron donor-containing mixture to 400 to 800 ° C and the washed product to 350 to 700 ° C is heated.