EP0046959B2 - Electrophotographic recording material - Google Patents

Description

The invention relates to an electrophotographic recording material composed of an electrically conductive layer support, optionally an insulating intermediate layer and a photoconductive layer system consisting of organic materials consisting of a layer optionally containing a binder with a charge-generating compound and a layer with charge-transporting compound which has a monomeric aromatic or heterocyclic compound is at least one dialkylamino group or two alkoxy groups, and a protective transparent cover layer in a thickness of 0.5 to 10 pm.

In the electrophotographic process for the production of copies known from US-A-2 297 691 and widely used today, a thorough cleaning of the photoconductor layer is always necessary after the transfer of the toner image developed dry on the photoconductor layer to the copy carrier. The cleaning is usually done by brushing or wiping the layer with suitable brushes or fabrics. In copying machines that work with liquid developers, the effect of mechanical cleaning is often enhanced by the use of a cleaning liquid. In addition to these cleaning operations, the photoconductive layer is also exposed to other influences that damage it. For example, it is subject to the action of the dry developer and the developer station (counter-tension) and, in the case of foot development, the action of the developer liquid. It is also exposed to the ionized air generated in the charging station. It is known that the required cleaning processes and the other influences mentioned lead to impairment or even mechanical damage to the photoconductor layer and thus to a reduction in its service life.

Recording materials with a photoconductive layer comprising at least one layer with a charge-generating and charge-transporting compound are known. For example, highly sensitive, organic photoconductor layers (DE-B-23 14 051) are used on conductive carrier films or tapes due to their high elasticity.

In particular, very highly sensitive photoconductor systems according to, for example, DE-A-27 34 288 can be used as endless belts because of their great flexibility, which can be guided over deflecting rollers with a relatively small diameter.

It is also known (US-A-2 901 348, US-A-4 148 637, DE-A-2 452 623). Protect photoconductor layers with an additional top layer made of inorganic or organic materials. The disadvantage of this is that they are used either on the less flexible layers consisting of or containing selenium or on generally less sensitive organic photoconductor systems. In addition, these cover layers must be mixed with silane couplers, such as chlorosilane, for better durability or additionally contain a photoconductive organic compound.

From "Research Disclosure", 1973, pages 67 to 70, cover layers on mono- or multiple photoconductor layers with inorganic or preferably organic photoconductor are known, which consist of a very specific combination of crosslinking agent with crosslinkable polymer or copolymer in a weight ratio of 1 to 9 . As crosslinking agents e.g. Prepolymers containing melamine formaldehyde and imino groups and, as crosslinkable polymers, those which have α, β-ethylenically unsaturated carboxylic acid or partial ester configurations. From this it can be seen that only these agents provide the physical properties which are essential and advantageous for a cover layer on a photoconductive layer.

From DE-A-27 33 052 an electrophotographic recording material of a certain structure is known which cannot be used industrially without a cover layer. The photoconductive multilayer is three layers of different thicknesses of different organic material. A top layer is applied to this, which is 20 pm thick and normally more than about 10 pm thick.

It is an object of the invention to provide the photoconductor systems which are made of organic materials and are highly light-sensitive, for example in a photoconductor double-layer arrangement, with a cover layer made of transparent materials which protect them from mechanical or possibly other adverse influences and which do not significantly impair the function of the photoconductor layer and generally Increase the service life of such systems.

The stated object is achieved by an electrophotographic recording material mentioned in claim 1, which is characterized in that the top layer consists of a surface abrasion-resistant organic binder made of phenoxy resin, purely acrylic resin, preferably of an aqueous dispersion of polyisocyanate and hydroxyl group-containing polyester or ether Polyisocyanate and hydroxyl group-containing acrylic or epoxy resin, or of polyisocyanate prepolymer or polyisocyanates with temporarily blocked isocyanate groups and that the top layer is 0.5 to 15.5 µm thick.

The result of this is that electrophotographic recording materials can be made available which, with almost the same photosensitivity, significantly improve the abrasion resistance and the service life.

The abrasion-resistant top layer can be applied by coating, dipping or also (electrostatic) spraying with subsequent drying and optionally hardening.

By increasing the abrasion resistance and thus the service life is achieved that the multi-layer arrangements can be used more profitably not only on flexible conductive substrates, but also on drums.

The electrophotographic recording material according to the invention is shown schematically by the attached FIGS. 1 to 4. For example, the photoconductive layer can be in the form of a single layer, as indicated in position 6 in FIG. 1. It can also be in the form of a double-layer arrangement which consists of a layer 2 containing charge carrier-producing compounds, as shown in FIGS. 2 and 3, and a layer containing charge-transporting compounds under the respective position 3, which is generally preferred . The conductive layer support is indicated with 1 in each case. An insulating intermediate layer is indicated at position 4. Position 5 shows a layer of charge generating compounds in dispersion. Position 7 indicates the protective cover layer according to the invention.

For example, aluminum foil, optionally transparent, aluminum vapor-coated or laminated polyester foil, is used as the conductive layer support, but any other layer support made sufficiently conductive can be used.

The insulating intermediate layer can be produced by a thermally, anodically or chemically produced aluminum oxide intermediate layer. It can also consist of organic materials. For example, different natural or synthetic resin binders are used that adhere well to a metal or aluminum surface and dissolve little when the other layers are subsequently applied, such as polyamide resins, polyvinylphosphonic acid, polyurethanes, polyester resins or specifically alkali-soluble binders, such as Example styrene-maleic anhydride copolymers. The thickness of such organic intermediate layers can be up to 5 pm, that of the aluminum oxide layer is largely in the range of 0.01-1 pm.

• Perylen-3,4,9,10-tetracarbonsäureanhydrid bzw. Perylen-3,4,9,10-tetracarbonsäureimidderivate nach DE-OS 2 237 539;
• oder gemäß DE-A-2 232 513 N,N'-Bis-(3-methoxypropyl)-3,4,9,10-perylentetracarbonsäureimid; polynukleare Chinone nach DE-A-22 37 678;
• cis-bzw.-trans-Perinone nach DE-OS 22 39 923;
• Thioindigo-Farbstoffe nach DE-A-2 237 680;
• Chinacridone nach DE-A-2 237 679;

Layer 2 or 5 has the function of a charge carrier generation layer. The compounds used to generate charge carriers determine to a particular degree the spectral sensitivity of the photoconductive system. Colorants of various classes can be used as charge-generating substances. Examples include:

• Perylene-3,4,9,10-tetracarboxylic anhydride or perylene-3,4,9,10-tetracarboximide derivatives according to DE-OS 2 237 539;
• or according to DE-A-2 232 513 N, N'-bis- (3-methoxypropyl) -3,4,9,10-perylenetetracarboximide; polynuclear quinones according to DE-A-22 37 678;
• cis-or-trans-perinones according to DE-OS 22 39 923;
• Thioindigo dyes according to DE-A-2 237 680;
• Quinacridones according to DE-A-2 237 679;

Condensation products from benzo-4,10-thioxanthene-3,1'-dicarboxylic anhydride and amines according to DE-A-2 355 075;

Phthalocyanine derivatives according to DE-A-2 239 924 and dyes, which by condensation according to the Bull.

Chem. Soc. Japan 25,411-413 / 1952 can be prepared from perylene-3,4,9,10-tetracarboxylic anhydride and o-phenylenediamine or 1,8-diaminophthalene, according to DE-A-2 314 051.

Dyes according to DE-A-2 246 255, 2 353 639 and 2 356 370 can also be used, for example.

The application of a homogeneous, densely packed layer 2 is preferably obtained by vacuum deposition. An advantageous layer thickness range of layer 2 is between 0.005 and 3 μm, since the adhesive strength and homogeneity of the vapor-deposited compound are particularly favorable here.

In combination with the intermediate layer or as a replacement for the intermediate layer, homogeneous, well-covering dye layers with thicknesses of the order of 0.1-3 μm can also be obtained by grinding the dye with a binder, in particular with highly viscous cellulose nitrates and / or crosslinking binder systems, for example polyisocyanate crosslinkable systems Acrylic resins, lacquers based on polyisocyanates and hydroxyl-containing polyester or ether, and by subsequently applying these dye dispersions 5 to the layer support, as can be seen from FIG. 4.

Compounds which have an extensive n-electron system are particularly suitable as the charge transport material in layers 3 and 6. These include, in particular, monomeric aromatic or heterocyclic compounds, such as those which have at least one dialkylamino group or two alkoxy groups. Oxdiazole derivatives, which are mentioned in German Patent 1,058,836, have proven particularly useful. These include in particular 2,5-bis (p-diethylaminophenyl) oxidiazole-1,3,4. Other suitable monomeric electron donor compounds are, for example, triphenylamine derivatives, more highly condensed aromatic compounds such as pyrene, benzo-condensed heterocycles, and also pyrazoline or imidazole derivatives (DE-B-10 60 714, 11 06 599), which also include triazole, thiadiazole and especially oxazole derivatives, for example 2-phenyl-4- (2-chlorophenyl) -5- (4-diethylamino) oxazole, as are disclosed in German patents 1,060,260,1,299,296,120,875.

The charge transport layer 3 has practically no photosensitivity in the visible range (420-750 nm). It preferably consists of a mixture of an electron donor compound with a resin binder if negative charging is to be carried out.

Layer 3 is preferably transparent. However, it is also possible that it does not need to be transparent, for example in the case of a transparent, conductive layer support. It has a high electrical resistance (≥ 10120) and prevents the discharge of electrostatic charge in the dark. When exposed, it transports the charges generated in the organic dye layer.

In addition to the charge generating and transporting compounds described so far, the added binder influences both the mechanical behavior such as abrasion, flexibility, film formation etc. and to a certain extent the electrophotographic behavior such as photosensitivity, residual charge and cyclic behavior.

Film-forming compounds such as polyester resins, polyvinyl chloride / polyvinyl acetate copolymers, styrene / maleic anhydride copolymers, polycarbonates, silicone resins, polyurethanes, epoxy resins, acrylates, polyvinyl acetals, polystyrenes, cellulose derivatives such as cellulose acetobutyrates etc. are used as binders. Post-crosslinking binder systems such as DD lacquers (for example Desmophen / Desmodur ^@ , Bayer AG), polyisocyanate-crosslinkable acrylate resins, melamine resins, unsaturated polyester resins etc. are also successfully used.

Because of the combined advantages (high photosensitivity, flash sensitivity, high flexibility), the use of cellulose nitrates, in particular the highly viscous types, is preferred.

The mixing ratio of the charge transporting compound to the binder can vary. However, the requirement for maximum photosensitivity, i.e. the largest possible proportion of charge-transporting compound and after crystallization to be avoided and increase in flexibility, i.e. as large a proportion of binders as possible, relatively certain limits. A mixing ratio of about 1: 1 parts by weight has generally been found to be preferred, but ratios between 4: 1 to 1: 2 are also suitable.

The thicknesses of layers 3 and 6 are preferably between about 3 and 20 pm.

Leveling agents such as silicone oils, wetting agents, in particular nonionic substances, are the usual additives. Plasticizers of various compositions, such as those based on chlorinated hydrocarbon or based on phthalic acid, are added. If necessary, sensitizers and / or acceptors can also be added to the charge transport layer, but only to the extent that the optical transparency of the charge transport layer is not significantly impaired.

In conjunction with the top layer according to the invention, additions of micronized organic powders of up to approximately 30% by weight, preferably 10% by weight, have also proven to be advantageous. To a certain extent, this improves the abrasion resistance and significantly improves the rougher, matt surface, in particular the adhesion promoter for the subsequent top layer. Preferred organic powders can be: micronized polypropylene waxes, polyethylene waxes, polyamide waxes or polytetrafluoroethylene and polyvinylidene fluoride powders.

Both non-crosslinking and postcrosslinking and self-crosslinking binders are suitable as surface abrasion-resistant organic binders for the top layer.

Phenoxy resin is mentioned as the non-crosslinking, organic binder.

Suitable postcrosslinking binders are: two-component systems made from crosslinking with aliphatic and / or aromatic polyisocyanate resin. Hydroxyl group-containing, saturated or unsaturated polyisocyanate resin-crosslinking, hydroxyl group-containing, saturated or unsaturated polyester or ether or polyisocyanate-crosslinking hydroxyl group-containing acrylic or epoxy resins, one-component systems made of air-drying polyurethane resin (polyurethane alkyd resin), or temporarily blocked isocyanate-curing polyisocyanates with er -Groups.

Pure acrylic resins, preferably aqueous dispersions, are suitable as self-crosslinking, optionally thermosetting binders.

It has also proven to be advantageous if the cover layer consists of a self-crosslinking polyisocyanate and the photoconductive layer contains a compound with hydroxyl groups.

The organic binders mentioned for the protective cover layer 7 are outstandingly suitable because of their homogeneous film formation and flexibility, their abrasion behavior and the application possibilities. The influence on the photosensitivity of the recording material is negligible.

The protective cover layer is optically transparent in a thin arrangement. The continuous layer produced on an organic photoconductor system in a double layer arrangement has a uniform thickness of about 0.5-10 μm, preferably of 0.5-5.0 μm. The film surface turns out to be smooth, which is necessary for optimal cleaning. The adhesion between the cover layer and the photoconductor system is also high enough to withstand mechanical influences, for example from the cleaning brush. The abrasion is significantly improved compared to the photoconductor system to be coated. It is essential that the cover layer behaves triboelectrically like the photoconductor layer. At 40―50 ° C as the storage temperature, the cover layer does not stick and no component exudes from the photoconductor layer. The cover layer also serves to prevent crystallization effects which can arise from contact with the photoconductor surface. The electrical conductivity of the cover layer is low enough not to influence the charge acceptance of the photoconductor. On the other hand, the materials mentioned allow the cover layer to be electrically permeable, so that charges can flow off from the surface when exposed to light, possibly down to a slight residual voltage. The electrostatic charge image remains until after exposure completely preserved for image development, which is necessary, otherwise the resolution of the copy decreases. The specific electrical resistance is not changed by moisture in the environment. Finally, the film surface is free of hydrophilic components so that the surface resistance is not changed by the climate.

The preferred application systems are coatings on a coating machine, preferably by means of flow application on, for example, photoconductor tapes, and spray technologies, optionally also electrostatically for applying the top layer on drums. When coating drums by dipping, it must be taken into account that the photoconductor system is solution-stable against the subsequent dip coating with top layer materials.

A particular embodiment of the recording material according to the invention consists in dispersing additives of micronized organic powders in the photoconductive layer; this significantly improves adhesion and abrasion properties.

In a further embodiment, photoconductive layers are coated with, for example, hydroxyl-containing binders, in particular with cellulose esters such as cellulose nitrates, with a polyfunctional aromatic / aliphatic polyisocyanate or polyisocyanate prepolymer, thereby producing an adhesion-promoting transition zone of curing between the photoconductive layer / cover layer.

The invention is explained in more detail with the aid of the examples, without being restricted thereto.

example 1

On the photoconductor double layer, which in the order given is made of aluminum-vaporized 75 pm thick polyester film as an electrically conductive layer support, a vapor-deposited layer of N, N'-dimethylperylimide (CI 71 129) and a charge transport layer of 2.5 bis (4- diethylaminophenyl) oxdiazole-1,3,4 (To) and highly viscous cellulose nitrate in a weight ratio of 65-35, a solution of the abrasion-resistant binders indicated in the table is applied by flow application with subsequent drying, which takes 5 minutes. The layer thicknesses of the individual protective cover layers with the different binders are in the range of 2 ± 0.5 pm. Both the photosensitivity and the abrasion behavior of the material with and without a top layer are tested under the same conditions. The results are summarized in the table.

• Zur Ermittlung der Hellentladungskurven bewegt sich die Meßprobe auf einem sich drehenden Teiler durch eine Aufladevorrichtung hindurch zu einer Belichtungsstation, wo sie mit einer Xenonlampe kontinuierlich belichtet wird. Ein Wärmeabsorptionsglas und ein Neutralfilter mit 15% Transparenz sind der Xenonlampe vorgeschaltet. Die Lichtintensität in der Meßebene liegt im Bereich von 40―60 µW/cm²; sie wird unmittelbar nach Ermittlung der Hellabfallkurve mit einem Optometer gemessen. Die Aufladungshöhe (U_o) und die photoinduzierte Hellabfallkurve werden über ein Elektrometer durch eine transparente Sonde oszillographisch aufgezeichnet. Die Photoleiterschicht wird durch die Aufladungshöhe (U_o) und diejenige Zeit (T_½) charakterisiert, nach der die Hälfte der Aufladung (U_o/2) erreicht ist. Das Produkt aus TlI2 und der gemessenen Lichtintensität I (pW/cm²) ist die Halbwertsenergie E_l/2 (µJ/cm²).

The photosensitivity is measured as follows:

• To determine the bright discharge curves, the measurement sample moves on a rotating divider through a charging device to an exposure station, where it is continuously exposed to a xenon lamp. A heat absorption glass and a neutral filter with 15% transparency are connected upstream of the xenon lamp. The light intensity in the measuring plane is in the range of 40-60 µW / cm ² ; it is measured with an optometer immediately after determining the light decay curve. The charge level (U _o ) and the photo-induced light decay curve are recorded oscillographically using an electrometer using a transparent probe. The photoconductor layer is characterized by the charge level (U _o ) and the time (T _½ ) after which half the charge (U _{o /} 2) has been reached. The product of TlI2 and the measured light intensity I (pW / cm ² ) is the half-value energy E _{l / 2} (µJ / cm ² ).

The residual charge (U _R ) after 0.1 sec, determined from the above bright discharge curves, is a further measure of the discharge of a photoconductor layer.

To test the abrasion behavior, the abrasion of both materials is measured on a standard abrasion device (Taber Abrasser type 352) under the following conditions:

The abrasion in g / m ² is the quotient of the gravimetrically determined abrasion in mg and the abrasion area.

Example 2

A photoconductive system as described in Example 1, but with 50 parts by weight of To, 25 parts by weight of polyester resin and 25 parts by weight of polyvinyl chloride / polyvinyl acetate copolymer in a thickness of approximately 10 / gm ² , is mixed with an aqueous polyacrylate -Dispersion (4% in H ₂ 0; acrylic acid ester / styrene copolymer) applied in one machine stroke by flow application. The thickness of this protective cover layer is about 0.5 pm after drying; with constant photosensitivity, the applied, glossy layer improves abrasion and increases the fatigue strength.

The values in the following table are determined analogously to Example 1:

Example 3

A photoconductive system produced in accordance with Example 2 is tested in a dry toner copier with regard to its surface properties and its photosensitivity. A magnetic brush device with a two-component toner mixture is used for development; the layer is guided past a rotating brush to clean the residual toner from the photoconductor surface. It shows that under the same copying conditions the copy quality is the same with and without the top layer. In the continuous copying test, after 5000 copies, strong surface films are already visible on the photoconductor layer without a protective cover layer and the surface is matte, on the other hand only minor surface films are visible on one with a cover layer and the surface is still shiny.

Example 4

To improve the abrasion behavior, 5 wt.%, Based on solids content, of micronized polyethylene wax (PE) or micronized polytetrafluoroethylene (PTEE) can also be dispersed into a charge transport layer composed of 65 parts of To and 35 parts of cellulose nitrate. In the subsequent coating on an aluminum-polyester layer support, which is vapor-coated with N, N'-dimethylperylimide, matt, homogeneous photoconductor layers are obtained.

Photosensitivity and abrasion are determined according to the information in Example 1.

Example 5

• Die homogenen Anordnungen werden einem Abriebtest gemäß Beispiel 1 unterzogen und ergeben:
• Photoleiterschicht+Deckschicht 0,95 g/m²
• Photoleiterschicht+PE+Deckschicht 0,5 g/_m ²

An aqueous dispersion of self-crosslinking, thermosetting pure acrylic resin is applied to the photoconductor layers described in Example 4 without and with micronized powder additive and is dried for about 10 minutes at 110 ° C. in a forced-air drying cabinet.

• The homogeneous arrangements are subjected to an abrasion test according to Example 1 and show:
• Photoconductor layer + cover layer 0.95 g / m ²
• Photoconductor layer + PE + cover layer 0.5 g / _m ²

This shows that micronized powder additives, especially in combination with cover layers, result in a significant reduction in abrasion.

Claims (8)

1. An electrophotographic recording material, composed of an electrically conductive layer support, an insulating interlayer, if appropriate, and a photoconductive layer system of organic materials comprising a layer which contains a binder, if appropriate, and a compound which generates charge carriers, and a layer containing a compound which transports charges, which is a monomeric aromatic or heterocyclic compound possessing at least one dialkylamino group or two alkoxy groups, as well as a protective transparent covering layer having a thickness of 0.5 to 10 pm, wherein the covering layer comprises a binder which is resistant to surface abrasion and is composed of a phenoxy resin, a pure acrylic resin, preferably from an aqueous dispersion, of a polyisocyanate and a polyester or polyether containing hydroxyl groups, of a polyisocyanate and an acrylic or epoxide resin containing hydroxyl groups, or of a polyisocyanate prepolymer or polyisocyanates having temporarily masked isocyanate groups, and wherein the covering layer has thickness of 0.5 to 5 um.

2. A recording material as claimed in claim 1, wherein the binder is a phenoxy resin.

3. A recording material as claimed in claim 1, wherein the binder is a two-component system comprising an aliphatic or aromatic polyisocyanate and a crosslinking saturated polyester or polyether containing hydroxyl groups, or comprising an aliphatic or aromatic polyisocyanate and a cross-linking acrylic or epoxide resin containing hydroxyl groups.

4. A recording material as claimed in claim 1, wherein the binder is a one-component system comprising an air-drying polyurethane resin or a polyisocyanate having temporarily masked isocyanate groups.

5. A recording material as claimed in claim 1, wherein the covering layer is composed of a self- crosslinking polyisocyanate and the photoconductive layer contains, as the binder, a compound containing hydroxyl groups.

6. A recording material as claimed in claim 1 or 5, wherein the photoconductive layer contains a finely micronized organic and/or inorganic powder in dispersion.

7. A recording material as claimed in claim 6, wherein the micronized powder is a polypropylene, polyethylene or polyamide wax, a polytetrafluoroethylene or polyvinylidene fluoride powder.

8. A recording material as claimed in claim 1, wherein cellulose nitrate is present as the binder for the photoconductive layer.

Images