DE1772288B2 - ELECTROPHOTOGRAPHIC RECORDING MATERIAL - Google Patents

Description

35

The invention relates to electrophotographic recording material, which contains a photoconductive layer of vitreous selenium and up to 1% by weight arsenic.

Vitreous se'en remains the most commonly used photoconductive material in the large-scale performed xerography (see. US-PS 29 70 906 and GB-PS 8 12 917) as it is able to hold an electrostatic charge for relatively long periods of time fixed and retained, provided it is not exposed to light. Also is Vitreous selenium is relatively sensitive to light compared to other photoconductive materials. In addition, vitreous selenium has such sufficient strength and stability that it is several 100 or can even be used some 1000 times. However, vitreous selenium is harmful to one Crystal growth, especially on its surface, is susceptible if the plate is in use is heated. This crystal growth in the selenium destroys its photoconductive insulating properties and represents a limit for the effective lifespan of a selenium plate. Even if the color sensitivity of (10 vitreous selenium is satisfactory, it is still exclusively on the blue or blue-green band the visible spectrum is limited.

Although vitreous selenium is a standard substance used in xerography, many can <> s its properties due to the addition of alloying elements which certain properties, such as color sensitivity, the Photosensitivity, thermal stability or the like increase. In British Patent 8 76 569 as well in US Pat. No. 2,822,300, the advantages of modifying vitreous selenium by the Addition of appreciable amounts of arsenic to achieve a wider color sensitivity range, to increase the overall photographic sensitivity and to improve the thermal stability of the photoconductive layer described. If it is also indicated in the literature references given above, that the arsenic is used in amounts of up to about 50% by weight, it is nevertheless known that Arsenic concentrations of more than approximately 5% by weight result in increased color sensitivity, but give the plate the property that it retains a high residual potential with a positive charge, in addition, there are high signs of fatigue caused by light. These last mentioned Appearances result in the formation of ghosting, which occurs after an extended, repetitive one Taking pictures occur and a very weak residual negative image in the background areas have as a consequence.

The known from DT-AS 10 77 976 xerography plate, which has a photoconductive layer from a uniform mixture of 0.5 to 20 wt .-% arsenic and vitreous selenium, also has the outlined disadvantages.

To achieve an optimal combination of photoconductive properties in a given Photoreceptors were developed from multi-layer photoreceptors to replace some of the above to overcome specified disadvantages. These structures can, for example, be a layer of selenium included, which is coated with a layer of a selenium-tellurium alloy. In British patent specification A structure of this type is written in 7 55 683, by means of which an improved sensitivity is thereby achieved is that a main layer or relatively thick layer of a vitreous selenium is used, which is with is coated with a thin layer made of an alloy of selenium and tellurium. If also If this structure has panchromatic sensitivity, it nevertheless quickly becomes due to a Destroys surface crystallization that occurs during operation of the xerograph. Additionally points this structure shows a high level of light fatigue. There were protective organic and inorganic coatings designed to prevent crystallization from occurring in the top layer. However, there is a major problem of these coatings in that they are incapable of doing so, within a wide range of Environmental conditions to work in a satisfactory manner.

From the foregoing it can be seen that in designing a photoreceptor for a certain area of application the physical stability, such as resistance to the action of heat under the operating conditions, in combination with optimal electrical Properties are essential factors in the selection of a particular photoreceiver.

The object of the invention is to provide an improved electrophotographic recording material create the lowest possible crystal growth in the photoconductive with good color sensitivity Has layer. This object is achieved by the invention.

The subject of the invention is thus an electrophotographic Recording material with a layer support and one - optionally with a halogen doped - photoconductive layer made of vitreous selenium and up to 1 wt .-% arsenic, which thereby is characterized in that the photoconductive layer in the direction from the support to the free surface a has increasing arsenic concentration, the arsenic concentration on the free surface more than Is 1.0 wt%

The recording material according to the invention is distinguished from known materials improved thermal stability and good photoconductive properties.

According to a preferred embodiment of the invention, the photoconductive layer contains between 0.1 and 1.0% by weight, preferably between 0.35 and 0.65% by weight arsenic, the arsenic concentration in Direction from the substrate to the free surface from 0 to 13% by weight, in particular from 0 to 5% by weight increases.

According to a particularly preferred embodiment, the photoconductive layer contains between 0.35 and 0.65% by weight, preferably 0.5% by weight, arsenic, with the arsenic concentration in the direction of the Layer support to the free surface increases from 0.1 to 1.5 wt .-%. This will be an excellent thermal stability and excellent photoconductive properties achieved

The thickness of the photoconductive layer depends on the application to which the alloy is put shall be. The alloy can be deposited on a substrate material, which for example can consist of a metal, a coated glass or plastic, a paper or the like. In addition, the alloy according to the invention can be used in multilayer structures, which will be discussed in more detail below or used alone as a separate photoconductive layer on any suitable Underlay can be used.

The thickness of the photoconductive layer is preferably 20 to 80 μm.

The advantages of this improved electrophotographic recording material are evident from the following Description and drawings.

F i g. Fig. 1 is a schematic representation of an embodiment of the electrophotographic of the present invention Recording material;

F i g. 2 shows typical heating cycles for vacuum evaporation of the alloys according to the invention compared to vitreous selenium;

F i g. 3 shows the arsenic concentration gradients for sections cut from three rolls, which have different arsenic concentrations.

In the figure! Reference numeral 10 denotes an embodiment of the electrophotographic according to the invention Recording material. This plate has a conductive layer support 11, for example Made of brass, aluminum, steel or the like. The carrier can have any thickness, whereby it is stiff or can be flexible and can have any desired shape, such as the shape of a film, a fabric, a plate, a cylinder, a roller or the like. The carrier can also consist of others Materials consist, for example, of a metallized paper, of plastic films, which are covered with a thin Layer of a metal, such as aluminum, or copper iodide coated, or made of glass that is coated with is coated with a thin layer of chromium or tin oxide. If necessary, the arsenic-selenium layer also be applied to a non-conductive substrate and electrostatically by known methods be charged, as they are common in xerography for photoconductive materials, the insulating Own documents. In addition, a carrier 11 can optionally be provided.

ίο The layer 12 consists of a photoconductive layer from selenium (with a degree of purity required for xerographic purposes), as it is for example in US Pat. No. 2,970,906. This selenium is in one with highly pure elemental arsenic Total concentration of about 0.1-1.0% is alloyed and has a composition gradient of arsenic which ranges from about 13% by weight on the exposed upper surface of layer 12 down to 0% Arsenic fluctuates at the substrate interface of the xerographic plate. The thickness of the layer 12 can only be 0.1 μ or up to 300 μ or more. For most technical areas of application, this thickness is if a single photoconductive layer is used, generally between about 20 and 80 microns.

Optionally, the arsenic-selenium layer may contain small amounts (about 10-10,000 ppm) of one Halogen, such as iodine or chlorine, to improve the electrical properties of the light-sensitive layer be doped. Such an embodiment is described in DT-OS 15 22711.

The crystallization of selenium and the selenium-arsenic alloys is of great importance with regard to the Storage as well as the service life of the drums in the machines. It has been found that both one Crystallization of the upper surfaces as well as the substrate surfaces in the form of spherical bodies which are generated by nucleation and growth of crystals if the selenium or the Selenium-arsenic alloy is excessively heated. It has also been found that the action of light in combination with heat accelerates the crystallization rate of selenium. The nucleation as well as the subsequent crystal growth are both at the interface and at the exposed upper surface of the selenium and selenium alloys pose a serious problem, however the more serious problem is the nucleation and subsequent crystal growth on the top Surface is. This is because crystallization surfaces on the upper surface cause the formation of a Plate, which has surfaces that have no electrostatic charge as a result of permanent Maintains conductivity of crystallized selenium.

ss Although this effect also occurs at the substrate interface can occur, it is not so severe in this case as partial crystallization of a The only consequence of the substrate interface is that this part of the plate is not part of the total thickness of the plate

do is suitable. A crystallization at the substrate interface however, it does not render the plate completely worthless for xerographic uses.

It has been found that at any suitable temperature the number of observed

<\ s cores decrease with increasing arsenic content. The addition arsenic also enables greater stability to environmental influences than selenium compared to the growth of crystal nuclei in the

1 / I Cd C *

Exposure to light, water, fingerprints, residual chemicals from the copy paper or the like. Has. Controlling the novel alloys of the present invention to have an increased amount of arsenic on the surface and a smaller amount of arsenic at the substrate interface takes advantage of the fact that greater thermal stability is required against crystallization on the surface of the xerographic plate. The new alloy according to the invention is therefore produced by controlling the evaporation conditions in such a way that essentially 100% selenium is condensed on the carrier substrate during the initial evaporation stages, with increasing amounts of arsenic being evaporated as the alloy evaporation progresses, so that a finished Plate is obtained having a steep concentration gradient extending from the substrate interface to the exposed top surface of the layer. This concept advantageously results in the use of a very small total amount of arsenic while still using the arsenic in its greatest concentration by providing a higher concentration at the point where the arsenic, both in terms of thermal stability and one, is used is effective over a wide range of color sensitivity. In virtually all cases, to achieve greatly increased thermal stability, the arsenic should be present at the surface in an amount of at least about 1.0%, while the amount at the substrate interface can actually be zero, but usually in an amount of about 0.1 % is present. The generally applicable method for the preparation of the novel compositions according to the invention consists in vacuum deposition while maintaining vacuums which ^{vary from approximately 10 "to 10;} Torr. The rate of deposition for a given heating time is critical in that the evaporation conditions must be controlled such that Most of the arsenic evaporated from the source or boat is evaporated during the end of the evaporation cycle so that a greater concentration of arsenic is obtained on the surface increasing amounts of arsenic are deposited during the later stages of the deposition cycle.

In the manufacture of the photoconductive alloys according to the invention, the substrate on which the photoconductive material is vapor-deposited is kept at a temperature between approximately 50 and 80.degree. If necessary, a plate heated with water or some other suitable device can be used to maintain a constant substrate temperature. In general, a 60 ^ -Selenium-arsenic alloy layer about 0.5 wt .-% arsenic contains, obtained when the vapor deposition for about 30 minutes χ 10 ^-5 Torr at a temperature of about at a vacuum of about 5 300 ⁰ C is carried out.

In GB-PS 8 76 569, US-PS 28 22 300 and DT-OS 15 22711 typical vacuum vapor deposition methods described. It should be noted, however, that the invention used Method, although it is similar to the methods described in the references cited above has a peculiarity in that the heating rate must be carefully controlled in order to do so the desired compositional gradient that would provide a significantly improved photoconductive layer with the above

s specified desired benefits allows in the Final product is obtained.

Typical heating cycles are shown in FIG Formation of a βΟ-μ layer from alloys containing approximately 0.1, 0.5 and 1.0% by weight of arsenic in selenium

ίο <- hold it, compared to making a usual one vitreous selenium shown. The curves apply to a vacuum of approximately 10 ■> Torr. As can be seen from curve I, there is a typical evaporation for Formation of a vitreous selenium in the fact that a source

is the selenium containing shot or pellets, is rapidly heated to about 150 ⁰ C in less than about 3 minutes. During this phase of the heating cycle, the selenium sample is mainly melted and degassed with very little condensation of the selenium on the substrate. Over the next 20 to 30 minutes, the rate of temperature increase increases at a much slower rate (see FIG. 2), with evaporation after approximately 30 to 35 minutes

2s has essentially ended. As can be seen from the curve I of selenium, a typical Aufdampfungserhitzungszyklus shows a maximum deposition temperature of about 250-290 ⁰ C. The curves II, III and IV show, respectively, increasing amounts of arsenic, which

yo to which selenium has been added. The amount of arsenic vary from 0.1, 0.5 to 1.0%. These amounts represent the total amounts of arsenic vapor deposited on the alloy. It can be seen that for increasing amounts of arsenic, the vapor deposition temperature increases, from about 300 ° C for 0.1% arsenic to about 350 ° C for 1.0% arsenic. The heating cycles represented by curves II, III and IV result in increasing amounts of arsenic which are released to the substrate at the end of the vapor deposition cycle or which are condensed on the substrate. In other words, this means that essentially pure selenium is condensed on the substrate in the period between approximately 0 and 5 minutes, with increasing amounts of arsenic emerging from the boat with increasing time. Over a period of 15 to about 30 minutes, the amount of arsenic condensed on a substrate or evaporated from the boat increases rapidly in proportion to the amount of arsenic in the boat, which in the end

so the surface amounts of arsenic present for the dre Typical curves shown between 1.0% arsenic on the surface of 0.1% arsenic alloy, 4.0% arsenic on the surface of the 0.5% arsenic alloy and approximately 8.0% arsenic on the surface of the alloy

ss containing 1.0% arsenic vary. The amount of arsenic ar the surface and at the interface can be controlled by the fact that the amount of arsenic in the alloy is varied or by changing the temperature of the alloy source during the vapor deposition cycle

becomes.

In compliance with the F i g. 2 reproduced i Typical evaporation rates will be an arsenic gradient from the photoconductive interface Alloy up to the exposed outer surface for three typical alloys, the 03, 04 and 0.8 ° Λ, respectively Total arsenic contained, preserved (see Fig. 3). Wii As can be seen from the curves, each of the three alloys shows a very pronounced concentration

5710

gradients starting from the alloy interface where about 0% arsenic is observed, and increasing to the surface at which the arsenic percentage is from about 1.2 up to 3.75% arsenic can fluctuate. The results shown by Fig. 3 were measured by means of an electron sample microanalyser.

The following examples illustrate the invention in specifically on the basis of a method for producing a thermally stable photoconductive Arsenic-selenium layer. Unless otherwise stated, the percentages relate to weight. These examples are intended to show the various preferred embodiments for producing the recording material according to the invention and a photoconductive layer which has a steep arsenic concentration gradient.

example 1

A starting alloy is produced by weighing elemental arsenic and selenium in an amount of 0.5% by weight arsenic and 99.5 % by weight selenium , whereupon the mixture is sealed in a silicon dioxide glass ampoule under vacuum. The mixture is then heated to about 460 ° C over a period of about 2 hours in a reciprocating oven and then cooled to room temperature. The homogeneous arsenic-selenium alloy obtained is then ground in a ball mill to a relatively fine-grained majc.K ... where the diameter of the individual particles is less than approximately 1 mm.

Examples 2 to 6

Four further starting alloys are produced separately using the method described in Example 1. These starting alloys contain υ, ι, 0.35, 0.65 and 1.0 % by weight of arsenic, the remainder being selenium .

Example 7

A photoconductive layer of 60 μm thick a total concentration of arsenic in selenium of 0.5 / o contains and is deposited on an aluminum roller, is made as follows:.

An oxidized aluminum substrate in the form of a cylindrical drum with a diameter of approximately 203 mm and a length of 305 mm is placed in a vacuum chamber in direct contact with a rotating, water- heated mandrel. The temperature of the roll is set to about 60 C. A source of the arsenic-selenium alloy which contains 0.5% by weight of arsenic and is prepared according to the method described in Example 1 ( sample weight = 120 g) is placed in an open stainless steel evaporation boat worai. the boat about 254 mm (10 inches) below the roller surface. The boat is connected to a source of electrical energy suitable for controlling the temperature of the boat. Torr evacuated, wöbe. ^ The drum is rotated at a speed of about rpm. During the first 2 to: 3_M utes dö heating is heated on the boat "ngf ^ah ^ 0 C. During this stage of the etching cycle, there is practically no evaporation. The sample melts inside the boat, if sufficient degassing occurs. Over the next 28 to 30 minutes, the temperature of the boat becomes substantially uniform at a rate of about 4 to 5 ° C per minute to one

S the final temperature is increased by approximately 300 ^° C. at the end of a total time of approximately 30 to 35 minutes. This ends the evaporation cycle. The electrical energy supply to the arsenic-selenium-containing boat is interrupted. The roller will

ίο then cooled and the vacuum vented. The roller coated with an arsenic-selenium alloy can then be removed from the chamber will.

Examples 8-11

Four further rolls, which contain 0.1, 0.35, 0.65 and 1.0% by weight of arsenic in selenium (produced according to the method of Examples 2 to 6), are carried out according to the method described in Example 7 while adhering to at the heating rates given below:

0.1%. arsenic

1. Heat to 150 ° C in about 3 minutes.

2. Continuation of the heating to 300 ⁰ C with a ' ^? Speed from 4 to 5 ° C per minute.

3. Hold at 300 ^° C. for a period of approximately 5 minutes, followed by cooling as in example 7.

1. Heat to 150 ° C in about 3 minutes.

2. Continuation of heating to about 310 ⁰ C at a rate of 4 ° to 5 ° C per minute.

3. Hold at 310 ^° C. for a period of 5 minutes, then cool down as in FIG

Example 7.

0.65% arsenic

1. Heat to 160 ° C in about 2/2 minutes.

2. Continue heating to 320 ° C at a ^4J rate of 4 to 5 ° C per minute.

3. Hold at 320 ^° C. for a period of approximately 5 minutes and cool as in example 7.

1.0% arsenic
1. Heat to 175 ° C in 2V ₂ minutes

2. Continuation of heating to about 350 ⁰ C mil a rate of 4 ° to 5 ° C per minute.

3. Hold at 350 ^° C. for a period of ί minutes and cool as in Example 7.

"° Example 12

A photoconductive layer of vitreous Seier of 60 μm thickness is applied to an aluminum roller in the manner described in Example 7 using selenium shot (3.2 to 4.8 mm) with a degree of purity required for xerographic purposes while observing the heating cycle given below applied:

1. Heat to 150 ° C in about 3 minutes. 2. Heat to 200 ⁰ C at a rate voi 4 to 5 ° C per minute.

3. Hold at 280 ^° C. for a period of approximately 5 minutes and cool as in Example 7

Example 13

The sieve rollers produced according to Examples 7 to 12 are each separately in an office copy

709521/31

^T 5

YII Δ ZOO

machine of the applicant (copy quality) tested. All Rollers make excellent copies with a high density and good resolution.

Six more rolls are being made for further testing. Two of these rolls contain 0.5% As (Example 7), two rolls contain 1.0% As (Example 11) and two rollers coated with a vitreous selenium do not contain arsenic (Example 12). The six Rolls are then heat treated in the following manner.

1. A roller of each composition is heated to 63 ° C for 240 minutes.

2. A roller of each composition is heated to 68 ° C for 100 minutes.

The samples are then microscopic for a possible nucleation and / or a possible Investigated crystal growth. The results are summarized in Table I.

Table I.

Heat treatment of the upper surface

% As heat treatment 240 minutes, 63 ° C

100 minutes, 68 ° C

Number of germs number of germs
Germs / cm ² knife, μ germs / cm ² diameter, μ

64

35

As can be seen from Table I, a considerable number of crystal nuclei are formed with one Sufficient size observed in a non-alloyed vitreous selenium, while the arsenic-selenium alloy samples showed no signs of crystallinity exhibit. The size of the seed crystals in Table I corresponds to the average observed for each roll Size.

Eleven further rolls containing 0.5% arsenic are produced according to the method of Example 7 and by means of an electron sample microanalyzer to study the concentration gradient of arsenic checked. The arsenic gradients of the eleven rollers (samples 1 to 11) are summarized in Table II:

Table II

Weight% arsenic

Upper

surface

Lower surface (substrate interface)

1
2
3
4th
5
6th
7th
8th
9
i0
11th

3.4

9.0

3.3

4.7

3.6

3.0

4.4

0.98

9.2

1.8

0.97

0.08

0.06

0.02

0.05

0.10

0.02

1 sheet of drawings

Claims (5)

Patent claims: 1. Electrophotographic recording material with a layer support and - optionally doped with a halogen - photoconductive layer made of vitreous selenium and up to 1 Wt .-% arsenic, characterized in that the photoconductive layer in the direction from The layer support has an increasing arsenic concentration towards the free surface, the arsenic concentration is more than 1.0% by weight on the free surface 2. Recording material according to claim 1, characterized in that it is in the photoconductive Layer between 0.1 and 1.0 wt .-%, preferably between 0.35 and 0.65 wt .-%, arsenic and the arsenic concentration in the direction from the substrate to the free surface from 0 to 13 % By weight, preferably from 0 to 5% by weight, increases. 3. Recording material according to claim 2, characterized in that it is in the photoconductive Layer between 0.35 and 0.65 wt .-%, preferably 0.5 wt .-%, arsenic and the Arsenic concentration in the direction from the support to the free surface from 0.1 to 1.5% by weight increases. 4. Recording material according to claim 1, characterized in that it is between 20 and 80 μm thick photoconductive layer contains. 5. Recording material according to claim 1, characterized in that the photoconductive Layer contains 10 to 10,000 ppm halogen, preferably chlorine. ι .s