DE2549181A1 - Process for the production of photoconductive, cadmium sulphide-like powdery materials - Google Patents

Description

EDUARD-SCHMID-STRASSE 2 D-8000 MUNICH 90

Konishiroku Photo
Industry, Co., Ltd.,
Tokyo, Japan

OUR SIGN: REGARDS:

. F / γΠΙ

MUNICH. THE

3rd NOV.

Process for the production of photoconductive, cadmium * sulfide-like powdery materials

The invention relates to the manufacture of a photoconductive one Powder of the cadmium sulfide type, e.g. of cadmium sulfide, Cadmium selenide, cadmium sulfide selenide and zinc selenide.

In the known method for producing a photoconductive one Powder was a mixture of a cadmium sulfide-like material, an activator such as copper or silver, for the formation of electron acceptor sites in the relevant material, a donor material, e.g. a halide to form donor sites and a flux such as cadmium chloride, sodium chloride and zinc chloride, calcined at temperatures above the melting point of the flux to control atomic valence. Photoconductive powders of various properties were made by changing the proportions of the various Components and / or the firing temperature.

-2-

609820/1132

A disadvantage of such known methods, however, is that there are very great difficulties in improving the 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 and their relationship to one another react. In addition, the dark resistance of the respective product is low and / or low "memory effect" great, even if the respective Product is endowed with the other desirable properties. In addition, these procedures are still has the disadvantage that the powder obtained in the course of the firing process with the formation of coarser Particle tends to stick together. So if the photoconductive material produced by such a method for image formation in the electrophotographic field, in image conversion or in image enhancement is used, only a low resolution image is obtained, since the surfaces of the formed photosensitive materials are not even and smooth.

In order to meet the difficulties outlined, a method for producing a photoconductive cadmium sulfide powder has already been developed, for example, 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) per 100 parts of cadmium sulfide used as a dispersant and in which the firing to 600 ⁰ C takes place (see. Japanese Patent application 28 814/70) at a temperature in the range of 400 °. The calcined product obtained by this process possesses

-3- 809820/1132

however, a relatively coarse particle size on the order of a few microns. Furthermore, the dark strength and the "memory effect" of the product obtained thereby insufficient. In fact, one has so far been able to be used as an image forming material in particular binder-containing electrophotographic recording materials, in which the photoconductive particles are dispersed in a resinous binder, cadmium sulfide-type photoconductive material satisfactory in practice cannot yet be produced.

The invention was based on the object of not having the described disadvantages of the known photoconductive Powder-coated photosensitive powder with excellent photoconductivity and very small particle size to manufacture.

The invention thus relates to a method for producing a cadmium sulfide-like photoconductive powder, which is characterized in that the cadmium sulfide-like substances in the absence of one Activator and burns in the presence of a dispersant.

This gives a cadmium sulfide-like material which has a very small particle size and is extremely light-sensitive photoconductive material.

Expediently, after the procedure has been carried out according to the invention, the dispersant is washed out with water.

-4-

609820/1132

As in the context of the method according to the invention in the production of the cadmium sulfide-like photoconductor powder if no activator is present, the method according to the invention is very simple. In addition, lets the photoconductor powder obtainable according to the invention particularly good as a light-sensitive photoconductor material due to its very small particle size in the photosensitive layers of electrophotographic Use recording materials in which the photoconductor powder is uniformly dispersed. With The help of such electrophotographic recording materials copies of images with excellent resolution are obtained, high contrast and - if at all - at most a slight haze. In addition, a shows the according to the invention electrophotographic recording material containing photoconductor powder that can be produced only one very little dark decay.

The cadmium sulfide-like materials which can be used in the process according to the invention are commercially available available as photoconductive powder. These are, for example, cadmium sulfide, cadmium selenide, Cadmium sulfide selenide or zinc selenide.

Suitable activators for cadmium sulfide-like photoconductor materials are, for example, the halides and sulfates or nitrates of gold, silver, copper and the like. These are activators that create acceptor sites in sufficient quantity in the crystals of the cadmium sulfide-like materials used can.

-5-

609820/1132

Useful donors are halides, e.g. ammonium chloride, or compounds of trivalent metals, e.g. of aluminum, gallium or indium. These are funds that allow the creation of donor positions able to activate sufficient amount in the crystals of the cadmium sulfide-like materials used.

Suitable fluxes are agents that work at the firing temperatures melt and melt the cadmium sulfide-like material. This is for example to halides such as cadmium chloride, zinc chloride, sodium chloride or potassium chloride.

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 firing temperatures during the firing process. The flow agents and dispersants used differ from one another (by definition) in whether or not they melt at the firing temperatures. Some substances can be used both as flow agents and as dispersants. That is, if the firing temperature is below the melting point of the material in question, it can be used as a dispersant. However, if the firing temperature is above the melting point of the material in question, it serves as a flow agent. For example, sodium chloride behaves as a flow agent at firing temperatures above 800 ^° C., since it melts ^{at 800 ° C.} Conversely, the sodium chloride can be used as a dispersant if the firing temperature is below the melting point.

-6-

6ÖS820 / 1132

The dispersants used according to the invention carry excellently contributes to the fact that the powdery calcined cadmium sulfide-like material particles do not stick together when melting, so that (thereby) the formation of a very fine photoconductive Powder of high sensitivity to light is favored.

The particle size of the light-sensitive obtained in the present invention Powder depends somewhat on the particle size of the respective cadmium sulfide-like starting material, the amount, type and particle size of the dispersant used and the state of dispersion. In particular, however, practice the type and amount of the dispersant exerts a relatively large influence on the particle size of the photoconductive powder.

The amount of added dispersant should expediently be 20% by weight - 6 or more, preferably more than 50% by weight of the cadmium sulfide-like material used be. The larger the amount of dispersant compared to the amount of cadmium sulfide-type used Material, the finer the photoconductive powder formed will be.

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

—7—

If, for example, cadmium chloride is used as a flow agent in the process according to the invention Sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, Potassium iodide, cadmium sulfate, zinc sulfate, sodium sulfate, Potassium sulfate and the like can be used. These substances melt at temperatures above the Melting point of the cadmium chloride and when using dispersion media such as water and alcohol, uniform dispersions. Furthermore, since they are water-soluble, they can be easily removed by just soaking them be washed out after burning. These dispersants are most expediently beneficial easy production of the desired photoconductive powder.

According to the invention, water or any 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 the atomic valence of the cadmium sulfide-like materials can be controlled by adding an activator increases the dark strength and sensitivity of the product. However, it has been shown that when using the fine powder obtained according to the invention with increasing amount of activator although the sensitivity increases, the dark resistance does not always increase, rather it even decreases can. In contrast, have the invention

-8th-

609120/1132

finely divided particles obtainable by firing in the absence of activators and in the presence of dispersants photoconductive materials not only have the same sensitivity (as can be achieved with the addition of activators is), but also a higher dark strength and thus a higher initial stress, which leads to the formation of high high-contrast images, as well as a lower "memory effect". Consequently, they are suitable according to the invention available photoconductive materials are excellent for use in electrophotographic Transmission method.

The theoretical mechanism of the effects achievable according to the invention has not yet been fully clarified, presumably however, it is based on the following conditions:

1. If, according to the invention, dispersants of the described Type, you get very 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) adsorb near the particle surface after firing in the presence of activators Water and the like, thereby lowering the dark strength.

3. It is known that cadmium sulfide-like crystal systems form during the firing process Form cadmium vacancies. Furthermore it is

-9-

609820/1132

is known that the region emitted as a result of exposure to light on such crystals Photoelectrons larger than the range of emitted photoelectrons when exposed to light on activated crystals. These cadmium vacancies can of course in dependence of their number to increase sensitivity as much or more as (than) the activators, like silver and copper.

According to the invention, the firing process can be carried out in the absence of superplasticizers and / or donors, if the dispersant consists, for example, of a halide (in this case part of the halide reacts with the cadmium sulfide-like starting material used and can be used in this form during the firing process actually act as a superplasticizer) and / or if part of the halide is furthermore in the course of the Mixing process behaves as a donor during the firing process. If, for example, sodium chloride is used as a dispersant cadmium sulfide is added without the addition of any superplasticizers or donors (cf. the following Experiments 2 and 7 in example 1), the following reaction takes place:

CdS + 2NaCl > CdCl ₂ +

Presumably the reaction product cadmium chloride acts as a superplasticizer or donor and the sodium sulfide during the firing process as well as sodium chloride as a dispersant.

-10-

609820/1132

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

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

-11-

609820/1132

example 1

Highly pure cadmium sulfide or cadmium sulfide selenide with a particle size of 0.05 to 0.5 microns (cadmium sulfide-like starting material) was mixed with cadmium chloride or potassium iodide as the flow agent, ammonium chloride as the donor, sodium chloride, sodium sulfate or cadmium sulfate as the dispersant and pure water or absolute ethanol as the dispersion medium (for the comparison sample medium also added copper (II) chloride as an activator). The amounts of the various ingredients are given in Table I. 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 respective dry mixture was transferred into an electric furnace and fired therein for 1 hour at a temperature of 500 ° to 700 ⁰ C (first firing). After finishing this firing, the fired 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 fired 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% ultrapure sulfur powder was added to the product, followed by thorough mixing of the respective mixture

-12-

609820/1132

was stirred. After stirring, the mixture was poured into a quartz tube, ^{fired for 20 minutes in a nitrogen atmosphere at a temperature of about 500 °} C. (second firing process), then cooled in a nitrogen atmosphere to a temperature of 200 ^° 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 No. 15 to 20) was determined by means of a Electron scanning microscope determined. The results obtained are shown in Tables I and below II included.

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 flow agent and 1.8 g of ammonium chloride as a donor in 40 ml of pure water was ground for β hours in a stirred ball mill and mixed, and then about 15 dried on a vaporization apparatus at a temperature of 14O ⁰ C h. The resulting dry mixture was admixed with 170 g of sodium chloride as a dispersant and 115 ml of absolute ethanol as a dispersion medium, whereupon the resulting mixture was ground again for 6 hours in a stirred ball mill and made uniform and then for about 10 hours on an evaporator at one temperature from 120 ⁰ C was dried. The dry mixture was crushed to the size of millet seeds, placed in a quartz tube and

-13-

60 9 820/1132

then burned for 15 minutes in an electric furnace at a temperature of 590 ^° C. in air. After cooling to room temperature, the fired product was thoroughly washed with pure water in the same manner as in Example 1 and then dried.

The dry product was then transferred to a quartz glass tube, then fired ^{for 10 minutes in a hydrogen sulfide atmosphere at a temperature of 500 °} C. and finally for 10 minutes in vacuo at a temperature of 500 ^{° C.} The fired 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 here are also included in Tables I and II.

Table I.

Outflow- Aktiva- Dona- Disper- Disper- Brenn

search for aisle means

No. Mate- (g) solution with rial 10-4 mol /

(50 g) ml (ml)

torma- gation- tempeterial medium medium rature (g) (g) (ml) ( ⁰ C)

1st 2nd stage

1 CdS CdCIp ' AI NHy ₁ Cl NaCl H ₂ O 580 500 5 / 2H ₂ O 4th 0.5 150 80 2 CdS - CdCIp
5 / 2HpO
10 * - NaCl H ₂ O 580 500 150 80 3 CdS - CdSO ₄ H ₂ O 700 500 150 80 4th CdS NH ₄ Cl
2.0 NaCl
150 H ₂ O
80 580 500

-14-

609820/1132

Table I continued

Outflow- Aktivasuch gang- means torlö no. mate- (g) solution

rial with 10 "

(50 g) moles / ml

(ml)

Dona- Disper- Disper-

tormaging

material medium medium

(g) (g) (ml)

Firing temperature

to

1. 2.Stu level

fe

CdSe

CdSSE

CdS

CdS

CdS

CdS

CdS

CdS

CdS

CdS

CdS

CdS

CdCIp · 5 / 2HpO 14 ²

CdCIp '5 / 2HpO 1Cr

CdCIp • 5 / 2H ₂ O

CdCIp. 5 / 2H ₂ O

CdCIp • 5 / 2H ₂ O

CdCI /

CuCl

^{5 /} f 2 ° 0.05 CdClp · CuCl, 5.00

NH ₄ Cl 1.8

NH ₄ Cl 5.0

NH ₄ Cl 0.5

JH ₄ CI 0.5

JH ₄ C] 0.5

NH ₄ Cl

NH ₄ Cl

NH ₄ Cl 0.5 NH ₄ Cl 0.5 NaCl 170

NaCl 100

NaCl 250 NaCl 50

NaCl 250

NaCl 1000

NaCl

NaCl

Na ₂ SO _- ,

NaCl

NaCl

150

NaCl

150

C ₂ H ₅ OH 115

H ₂ O 80

C ₂ H ₅ OH 80

H ₂ O

40

H ₂ O 120

H ₂ O 400

H ₂ O

80 H ₂ O

80 C ₂ H ₅ OH

80 H ₂ O

80 H ₂ O

80

H ₂ O 80

590

580

580

580

580

580

650

700

600

500

580

580

-15-

809820/1132

Table I continued

Ver
search
No. The end-
gangly
mate-
rial
(50 g) Flow
middle
(G) assets
torlö
sung.
with 10 ^H.
Moles / ml
(ml) Dona
torma
material
(G) Disper
greed
middle
(G) Disper
sion
medium
(ml) Burned
temperature
1. 2.
Stu- stu
fe fe 17th CdS - CuCl ₂ - NaCl CpHt-OH 580 500 5.00 150 80 18th CdS CdCIp
5 / 2H ₂ ¹ O NH ₄ Cl
0.5 - H ₂ O
80 580 500 19th CdS CdCIp
5 / 2H ₂ O CuCl ₂
0.50 NH ^ Cl
0.5 - H ₂ O
80 580 500 20th CdS CdCIp
5 / 2Hp ¹ O
15 ^ CuCl ₂
5.00 NH ₄ Cl
2.0 H ₂ O
80 580 500 Table II

attempt

Particle size (η)

0-0.5 0.5-1 1-2 2-5 5-10 10-20 20-30 30-40 40-number of the particles

24 33
28
11

2
12th

4th 33 57

53 63 43 46 18 4 68 18 58 43

18th

21

26th

76

82

16

38

5 2 8

17 6

12 4

30th

10

-16-

609820/1132

- 16 Continuation of Table II

Ver
search
No. 0-0.5 0.5-1 Particle size ( μ )
1-2 2-5 5-10 10-20
Number of particles 1 - - 20-30 30-40 40- 11 41 54 4th 3 - - - - - - 12th 14th 63 20th 1 - - - - - 13th 21 68 10 - - - - - - - 14th 47 43 10 1 - - - - 15th 22nd 47 30th 4th - - - - - 16 18th 46 32 8th - - - - - 17th 7th 63 22nd 12th 33 28 - - 18th - 3 10 8th 28 29 19th 5 19th - - - 24 40 23 10 2 20th 25th 11

The results contained in Table II show that in the experiments according to the invention by firing in the presence the specified dispersants and products obtained in the absence of activators are low Have particle size of about 1 micron diameter and that their particle size distribution by changing the Quantities of the cadmium sulfide-like starting material, donor, flow agent and dispersant used can be controlled. In addition, the excellent crystal structure was obtained according to the present invention Products confirmed by X-ray diffraction.

In contrast, those fired in the presence of activators or in the absence of dispersants Comparative products of typically large average particle size of 10 to 20 microns.

-17-

609820/1132

Example 5

3.5 g of a commercially available alkyd resin with a solid content of 50% and 3 ml of butyl acetate were added to each 5 g of the photoconductive powders produced according to the invention in Examples 1 and 2 and the comparison powder added, followed by dispersing the respective mixture by an ultrasonic dispersing process a photosensitive coating liquid was prepared. The respective light-sensitive Coating liquid was thus applied to the surface of a 0.2 mm thick aluminum plate by means of a wire bar applied so that after drying and a heat treatment a layer of 20 microns thick is formed became. In this way, Samples Nos. 21 to 34 and Comparative Samples 35 to 35 of the present invention became 40 manufactured. The test specimens according to the invention contained the light-sensitive powders of Experiment No. 1 to 14, the comparative test specimens the photosensitive powders of tests 15 to 20.

The values for the surface potential of the test specimens and comparison test specimens obtained by means of a rotating disk electrometer were measured, as well as the "memory effect" and fog that occurs in actual use in a transfer copier with magnetic brush development were found in Table III below. In the table:

1. "Initial potential" is the surface potential of the DUTs and comparison test objects 5 see after charging the test objects and comparison test objects

-18-

609820/1132

linge by means of a corotron charging device with a charge voltage of -6 kV;

2. "Light sensitivity" means the half-life in see, which is the initial voltage of the test specimens and comparison test specimens when their surfaces are irradiated with a tungsten lamp with a light intensity of 5 lux to half the potential, and

3. "Residual potential" is the surface potential of the test specimens and comparison test specimens after a 30 lux-sec exposure with a tungsten lamp.

The haze and "memory effect" were determined on the basis of the image copies produced with the copier mentioned. The corotron charging station was set to a charge voltage of -5.7 kV. To the A bias voltage of -200 V was applied to the magnetic brush.

-19-

809820/1132

Table III 2.0 60 image
veil "memory
Effect" Check
ling
No. Potential properties
Initial light temp residual potential
potential sensitive (V)
tial (V) speed (see) 2.2 68 weak small amount 21 450 2.5 46 weak small amount 22nd 476 1.9 48 weak small amount 23 321 1.2 40 weak small amount 24 352 1.7 65 weak middle 25th 300 1.9 58 weak middle 26th 310 1.9 70 weak small amount 27 432 2.2 60 weak middle 28 307 2.4 72 weak small amount 29 412 2.5 62 weak small amount 30th 278 2.0 70 weak small amount 31 370 1.9 72 weak middle 32 350 2.2 75 weak small amount 33 463 2.1 62 weak small amount 34 364 1.7 40 weak small amount 35 324 2.0 43 weak middle 36 220 2.8 120 weak middle 37 238 2.5 178 strong great 38 363 3.0 138 strong great 39 403 strong great 40 308

It can be seen from Table III that the photosensitive powders which can be prepared according to the invention are outstanding in the context of electrophotographic transfer processes because they have a high dark resistance, a high initial potential that

-20-

609820/1132

is required for the production of high-contrast image copies, have the same sensitivity as the photoconductive reference powders fired in the presence of activators, have a low "memory effect" and thus do not produce dull images even with repeated and continuous copying processes. In contrast, the comparative powders produced without the addition of dispersants of the type described consisted of photoconductive powders of large particle size which, when copied with a transfer copier, have a high residual potential and show a strong fog and "memory effect". Consequently, the comparative powders are not suitable for practical use. In addition, the photoconductive powders fired in the presence of activators and dispersants have also proven unsuitable for use in electrophotographic transfer copiers, since _{the initial potential N} decreases and the "memory effect" / increases as the amount of activator increases. Furthermore, the particle size is also large here.

+) strong

-21-

609820/1132

Claims (8)

Claims 1. Process for making photoconductive cadmium sulfide-type Powder, characterized in that cadmium sulfide-like starting materials without Addition of an activator and burns in the presence of a dispersant. 2. The method according to claim 1, characterized in that the burning process in the presence of not less as 20 parts by weight of dispersant per 100 parts by weight of cadmium sulfide-like starting material performs. 3. The method according to claim 1, characterized in that the firing process is carried out in vacuo or in nitrogen gas, sulfur gas or hydrogen sulfide gas atmosphere performs. 4. The method according to claim 1, characterized in that the burning process in the presence of a donor performs. 5. The method according to claim 1, characterized in that the burning process in the presence of 0 to 10 Part (s) by weight of donor per 100 parts by weight of cadmium sulfide type Performs starting material. 6. Process for producing photoconductive cadmium sulfide-like Powders, characterized in that a cadmium sulfide-like starting material is used without the addition of an activator and in the presence of one -22- 809820/1132 Dispersant burns and that the burned product to remove the water-soluble contained therein Wash ingredients with water. 7. The method according to claim 6, characterized in that the washed product is reburned. 8. A process for preparing a photoconductive cadmium sulfide-like powder, characterized in that one burns a cadmium sulfide-like starting material without addition of an activator and in the presence of a dispersant at a temperature of 400 ° to 800 ⁰ C, that the fired product to remove the water-soluble ingredients contained therein washed with water and the washed product that burns again at a temperature of 350 ° to 700 ⁰ C. 609820/1132