WO1995006274A1

WO1995006274A1 - Charge transport polymer, a charge transport layer, and a photoconductive member comprising said charge transport polymer

Info

Publication number: WO1995006274A1
Application number: PCT/EP1994/002701
Authority: WO
Inventors: Johan Bernard Reesink; Paulus Pieter De Wit
Original assignee: Akzo Nobel N.V.
Priority date: 1993-08-20
Filing date: 1994-08-12
Publication date: 1995-03-02

Abstract

The invention pertains to a charge transport polymer containing a dibenzocycloalkenylidene group which is covalently bonded to the polymer chain as side group. This charge transport polymer is utilised in the transport layers of photoconductive members used in photocopiers and printers. It was found that polymers containing charge transport compounds according to the invention have excellent charge transporting properties. The invention further pertains to a multilayer photoconductive member with a charge transport layer comprising a polymer according to the invention.

Description

CHARGE TRANSPORT POLYMER, A CHARGE TRANSPORT LAYER, AND A PHOTOCONDUCTIVE MEMBER COMPRISING SAID CHARGE TRANSPORT POLYMER

The invention pertains to charge transport compounds containing a dibenzocycioalkenylidene group. Such charge transport compounds are utilised in the transport layers of photoconductive members for use in photocopiers and printers.

Such charge transport compounds have been described in GB-A-2250742 and FR-2603713. For instance, the charge transport compounds according to GB-A-2250742 satisfy formula 1:

wherein: Ar stands for an aromatic compound,

Ri represents -H, Cχ_4 alkyl or halo, and R- represents -H, Cχ_4 alkyl or halo.

These compounds may be mixed into a polymeric matrix as a so-called solid solution. However, there are several drawbacks to charge transport layers based on solid solutions. The charge transport compounds having to be dissolved in a polymeric matrix, the choice offered is restricted on account of their generally poor solubility. This poor solubility may give rise to the formation of crystallites as a result of segregation of the transport compound in the polymeric matrix. This gives problems especially during processing, when drying the wet-coated layer. The long-term stability, of these solid solution systems also leaves something to be desired. It has been attempted to covalently bond charge transport compounds to the polymeric matrix to form so-called charge transport polymers (CTPs). For instance, several publications describe polymers having carbazole derivative-containing side chains, e.g.: EP-A-0462406, JP 48594483, DT 2 522993, JP 76003 759, US 3 994994, US 4 125 534, GB 1 075 628, and JP 62070408.

However, the CTPs developed up to now have charge transport properties which are inferior to those of the solid solution systems. CTPs have to meet a wide range of requirements. For instance, they must have sufficient mechanical strength and be wear-resistant. Preparing a smooth film from the CTP should not give any problems. In addition, the CTP has to be transparent to the light to be used. The CTP layer should also adhere properly to the supporting layer. It should have low dark decay, i.e., its electrostatic surface charge should be well retained in the dark. The CTP should be chargeable to a sufficiently high level, be capable of proper hole or electron transport, and be without an injection barrier vis-a-vis the generation layer. Further, the residual charge remaining in the CTP after exposure should be as low as possible. Of course, the layer must be readily cleanable, so that toner particles and paper dust can be properly removed. The invention has for its object to provide CTPs which have not only the above-mentioned properties but also charge transport properties comparable with those of solid solution systems.

The invention is characterised in that the charge transport compound is covalently bonded to a polymer chain as side group and satisfies formula 2 below: When the transport compound according to formula 2 is bonded to polyesters, polycarbonates or polyurethanes, it should be OH-functionalised in advance. Between the X-group and the two OH-groups there may be all sorts of spacer groups. Examples of these HO-X-OH groups include:

wherein x and y represent an integer in the range of 1-6.

To prepare charge transport polyesters, OH-functionalised transport compounds as disclosed above may be polymerised with dioic acids, dioic acid chlorides or esters of dioic acids. As examples of these may be mentioned: terephthaloyl chloride, terephthalic acid, adipic acid, adipoyl chloride, esters of terephthalic acid, esters of adipic acid, 1,4-cyclohexane dicarboxylic acid, etc. Diols which do not contain any charge transport groups may of course be copolymerised.

To prepare charge transport polyurethanes, OH-functionalised transport compounds such as disclosed above may be polymerised with diisocyanates. As examples of these may be mentioned: hexamethylene diisocyanate, paraphenylene diisocyanate, xylylene diisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate. Again, diols which do not contain any charge transport groups may be copolymerised.

To prepare charge transport polycarbonates, OH-functionalised transport compounds such as disclosed above may be polymerised with bischlorofor iates of, say: bisphenol A, bisphenol S, hydroquinone, and oligomers thereof. Alternatively, the polycarbonates may be obtained by means of transesterification of, e.g., diphenyl carbonate. Again, diols which do not contain any charge transport groups may be copolymerised.

When the transport compound according to formula 2 is bonded to polyamides, polyureas or polyimides, the transport side group should be NH -functionalised in advance. Between the X-group and the two NH -groups there may be all sorts of spacer groups. Examples of these H N-X-NH₂ groups include:

H₂N CH CH₂ NH₂ H?N NH₂ H

\ CH₂ / \ N/ \ CH / \ CH - CH /₂ (C IH )_V

I I I

(CH₂)_X ,H₂N - CH₂ - C - CH₂ - NH₂

0 (CH₂)_X

I I o

wherein x and y represent an integer in the range of 1-6.

To prepare charge transport polyamides, NH -functionalised transport compounds such as disclosed above may be polymerised with dioic acid chlorides or esters of dioic acids. As examples of these may be mentioned: terephthaloyl chloride, adipoyl chloride, esters of terephthalic acid, esters of adipic acid, 1,4-cyclohexane dicarboxylic acid, etc. Of course, diols which do not contain any charge transport groups may be copolymerised.

To prepare charge transport polyureas, NH -functionalised transport compounds such as disclosed above may be polymerised with diisocyanates. As examples of these may be mentioned: hexamethylene diisocyanate, paraphenylene diisocyanate, xylylene diisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate. Of course, diamines which do not contain any charge transport groups may be copolymerised. To prepare charge transport polyimides, NH₂-functionalised transport compounds such as disclosed above may be polymerised with dioic anhydrides. As examples of these may be mentioned: pyromellitic anhydride, ethylene glycol bis(4-trimellitate anhydride), 4,4'-oxydiphthalic anhydride, 3,4,3' ,4'-diphenyl tetracarboxyl anhydride, and 3,3' ,4,4'-benzophenone tetracarboxyl dianhydride. Again, diamines which do not contain any charge transport groups may be copolymerised.

To incorporate transport compounds according to formula 2 into polyethers, the transport side groups must be functionalised with a single epoxy group. Alternatively, copolymers may be produced with these functionalised groups.

To incorporate transport compounds according to formula 2 into polymers which polymerise under the influence of radicals, the transport side groups must be functionalised with a single vinyl or acrylate group. Alternatively, copolymers may be produced with these functionalised groups.

In order to optimise their mechanical or charge transporting properties, additives may be added to the charge transport polymers according to the invention.

As stated earlier, these charge transport polymers may be utilised in the transport layers of multi-layer photoconductive members for use in electrophotography. As a rule, they have the following construction: a) a substrate b) a generation layer c) a charge transport layer.

If so desired, there may be additional layers, such as an anti-curling layer beneath the substrate, adhesive layers, and a coating. The substrate is made up of an electrically conductive material, which may be either a solid metal, e.g., aluminium, preferably in the form of a drum, or a composite material in the form of a drum or a belt which is composed of an insulating substrate onto which an electrically conductive coating of, say, aluminium has been applied. Since the CTPs according to the present invention are flexible, they are pre-eminently suited to be used in photoconductive members which are guided around rollers in the form of a seamless belt. The multi-layer photoconductive members according to the invention are even suitable for use when small rollers are employed in small-sized photocopiers and printers. The skilled person will know which substrates are suitable for use, so no further elucidation is required here.

The generation layer contains a charge generating compound. Such compounds may be of an inorganic as well as an organic nature. When use is made of inorganic material, it is generally present in the form of either particles dispersed in a binder or a homogeneous film produced by, say, vacuum vapour deposition. The most commonly employed inorganic material is selenium. When organic material is used, it may be present in the form of a film-forming polymer, such as polyvinyl carbazole, polyvinyl pyrine, or in the form of particulate pigment particles dispersed in an organic binder layer, such as the bisazo pigments mentioned in US-A-4286040, Alternatively, the charge generating compounds present may be distributed on a molecular level. The advantage of such layers is that they can be much thinner (1-2 micrometers in thickness) and smoother by nature than the pigment binder layers. Moreover, the grinding required in other preparative processes may be omitted here. Charge generating layers of the type indicated here have been described in, int. al . , US 4 123 270, US 4286040, and GB 1 171 355. The CTPs according to the invention are pre-eminently suited to be used in combination with these charge generation layers, since the former permit the whole to be 10

sufficiently highly charged in a uniform manner. Such is essential when using these vulnerable generation layers of not more than 1-2 micrometers in thickness. Generation layers are known to the skilled person and require no further elucidation here.

The invention further relates to a multi-layer photoconductive member with a charge transport layer comprising a polymer according to the invention. The thickness of this charge transport layer may range from 1.0 to 50 micrometers.

Also, there are photoconductive members in which the generation layer and the charge transport layer have been replaced by a single-layered system performing both functions. The charge transport polymers according to the invention are also suitable for use in a single- layered system. Of course, in that case charge generating compounds will have been added to the charge transport polymer. The invention further pertains to a single-layered photoconductive member comprising a charge transport polymer according to the invention.

The invention will be further illustrated with reference to a number of unlimitative examples, which are submitted solely for a better understanding of the invention.

EXAMPLES

Example 1: the preparation of CTP 1

Synthesis of 9(4-(bis(2-hydroxyethyl)amino)benzylidene)fluorene

The synthesis of

4[2,2'-bis((1,1-dimethylethyl)dimethylsilyl)oxy]aminobenzaldehyde has been disclosed in EP 0350 112. 11

To 7,2 g (300 mmoles) of sodium hydride in 100 ml of dry THF were added, under nitrogen, at room temperature, in 1 hour, 49,8 g (300 mmoles) of fluorene in 150 ml of dry THF. The reaction mixture was refluxed for 30 minutes. After cooling to 10°C there were added, in 1 hour, 114,3 g (300 mmoles) of

4[2,2'-bis((1,1-dimethylethyl )dimethylsilyl)oxy]aminobenzaldehyde in 150 ml of dry THF. After stirring overnight at room temperature 150 ml of methanol were added dropwise, after which the mixture was poured into 2 1 of ice water. The layers were separated, the water layer was extracted with three portions of 500 ml each of ether, the collected organic layers were washed with two portions of 250 ml each of brine and then dried on anhydrous magnesium sulphate. The organic layer was filtered and concentrated by evaporation. The residue was suspended in 1,5 1 of methanol. After the addition of 15 ml of 4N hydrochloric acid the mixture was stirred overnight. The reaction mixture was concentrated by evaporation, and 500 ml of 10% sodium carbonate solution and 500 ml of ethyl acetate were added to the residue. The layers were separated, and the water layer was extracted with two portions of 250 ml each of ethyl acetate. The ethyl acetate layer was washed with 150 ml of brine and dried on anhydrous magnesium sulphate. The organic layer was filtered and concentrated by evaporation. The residue was crystallised from 600 ml of ethyl acetate and 200 ml of hexane. Yield: 88,3 g (82%); melting point: 134-137°C.

Synthethis of CTP 1

Added to a mixture of 5,88 g (16,5 mmoles) of

9-(4-(bis(2-hydroxyethyl)amino)benzylidene)fluorene, 2,56 g (12,6 mmoles) of terephthaloyl chloride, and 0,75 g (4,1 mmoles) of adipoyl chloride in 35 ml of dry THF at 10-15°C were 4 ml of pyridine. The reaction mixture was stirred at room temperature for 1 hour and at 50°C overnight. After cooling to room temperature the reaction mixture was diluted with 50 ml of THF and filtered. The filtrate was poured 12

into 1 1 of methanol, the precipitated polymer was filtered off, washed with methanol, and dried. Yield: 7,11 g (90%); Mw = 7300; Tg = 105°C.

Example 2: the preparation of CTP 2

CTP 2 was prepared in the same manner as CTP 1, use being made of: 9,68 g (27,1 mmoles) of

9-(4-(bis(2-hydroxyethyl)amino)benzylidene)fluorene, 2,84 g (14,0 mmoles) of terephthaloyl chloride, 2,48 g (13,6 mmoles) of adipoyl chloride, and 6,5 ml of pyridine. Yield: 12,2 g (93%); Mw = 13 100; Tg = 89/98°C.

Example 3: the preparation of CTP 3

A mixture of 1,79 g (5,00 mmoles) of

9-(4-(bis(2-hydroxyethyl)amino)benzylidene)fluorene, 1,07 g (5,00 mmoles) of diphenyl carbonate, and 20 mg of titanium(IV) n-butoxide was heated at 120°C for 1 hour, at 120°C and 16 mm Hg for 3 hours, and then at 150°C and 0,1 mm Hg for 1 hour. After cooling the reaction mixture was dissolved in 20 ml of THF, filtered, and poured into 250 ml of methanol. The precipitated polymer was filtered off, washed with two portions of 50 ml each of methanol, and dried. Yield: 1,85 g (96%); Mw = 5500; Tg = 97/108°C.

Example 4: the preparation of CTP 4

CTP 4 was prepared in the same manner as CTP 1, use being made of: 4,90 g (13,7 mmoles) of

9-(4-(bis(2-hydroxyethy1)amino)benzylidene)fluorene, 8,61 g (14,1 mmoles) of terephthaloyl chloride, 2,54 g (13,7 mmoles) of adipoyl chloride, 2,55 g (41,1 mmoles) of ethylene glycol, and 13,3 ml of pyridine. Yield: 12,8 g (88%); Mw = 13 300; Tg = 60/71°C. 13

Example 5: the preparation of CTP 5

To a solution of 3,77 g (10,3 mmoles) of 4,4'-isopropylidene diphenol bis(chloroformiate) and 3,67 g (10,3 mmoles) of

9-(4-(bis(2-hydroxyethyl)amino)benzylidene)fluorene in 30 ml of dry THF were added dropwise, over 1 hour and under nitrogen, 2,5 g of dry pyridine in 10 ml of THF. The reaction mixture was stirred overnight at room temperature, filtered, and poured into 1 1 of methanol. The precipitated polymer was filtered off, washed with methanol, and dried. Yield: 6,46 g (97%); Mw = 41 200; Tg = 119/124°C.

0,8 g of the prepared polymers was dissolved in 4 g of THF. Under a nitrogen atmosphere, a film was dip coated onto a PET substrate provided with a vacuum vapour deposited aluminium layer (0,5 micrometers) and a vacuum vapour deposited layer of alkylaryl substituted perylene diimide as generation layer. The coated film was dried for about 8 hours in a vacuum oven at a temperature below Tg. Preparing a smooth film with proper adhesion and high mechanical strength from the CTPs according to the invention proved to be quite feasible.

Comparative example:

For reasons of comparison a charge transport compound (CT*) according to the formula below such as disclosed in GB-A-2 250 742 was tested in a solid solution system: 14

\ /

N

C / \ c c c c

\ / c

I

1 CH

II

C / \ c • - c c - c

/ \ / \ c c-c c

\ / \ / c = = c c = c

This 9-(4-[dimethylamino]benzylidene)fluorene is available from Bader Chemicals (Aldrich). The compound was recrystallised from ethanol under nitrogen. CT* was mixed into a 6%-polymer solution of Lexan 141^® (ex General Electric) in THF (Lexan/CT* ratio is 5/6). In the same manner as described above a film of this was coated onto a PET substrate provided with a vacuum vapour deposited aluminium layer and a generation layer as disclosed above.

Both the CTP films and the CT* film had their charge transport properties determined. To this end, the films were electrostatically charged (1 mC/m*) and then exposed to white light. The dark decay (DD) was defined as:

V_n - Vς X 100 (in %) Vθ wherein: VQ = potential immediately after charging, V5 = potential 5 seconds after charging. 15

Indicative of the concentration of trapped charge ρt (number of holes/cm^) after exposure is Q, with Q being independent of the layer thickness:

Q = / Vua.

wherein: V_na = potential after exposure, d = thickness of the CTP layer (μm) , e_r = relative dielectric constant.

The results of these measurements have been compiled in TABLE I, which also lists the type of polymer used and the polymer composition (i.e., the monomers copolymerised together with the charge transport group-containing monomer).

TABLE I film type of monomers DD Q polymer (%)

CTP 1 polyester 25% adipoyl chloride 93,7 2,4

75% terephthaloyl chloride

CTP 2 polyester 50% adipolyl chloride 96,0 2,4

50% terephthaloyl chloride

CTP 3 polycarbonate diphenyl carbonate 92,5 2,4

CTP 4 polyester 25% adipoyl chloride 91,4 2,4

75% terephthaloyl chloride ethylene glycol

CTP 5 polycarbonate Bisphenol A chloroformiate 93,7 2,4

CT* polycarbonate 91,3 4,4

TABLE I shows that the CTPs according to the invention have charge transport properties which are at least comparable with solid solution systems and even have lower charge trapping than a system with comparable charge transport compounds in the form of a solid solution.

Claims

16CLAIMS:

1. A charge transport compound containing a dibenzocycioalkenylidene group, characterised in that the charge transport compound is covalently bonded to a polymer chain as side group and satisfies formula 2 below:

P Q

\ / X

wherein: X stands for -N- or -0-,

Y is a conjugated system,

P and Q are radicals of the polymer to which the side group is bonded, n is 1 or 0,

Ri represents -H, an alkyl group having 1-4 carbon atoms, a halo-substituted alkyl group having 1-4 carbon atoms, -halogen, an alkylene group having 1-6 carbon atoms which is bonded on either side to a C atom of the benzene ring, an alkenylene group having 1-6 carbon atoms which is bonded on either side to a C atom of the benzene ring, an alkenyldiene group having 1-6 carbon atoms which 17

is bonded on either side to a C atom of the benzene ring, an al enyltriene group having 1-6 carbon atoms which is bonded on either side to a C atom of the benzene ring, an electron donating group, Rϊ represents the same groups as Rι but may be selected independently from Ri.

A charge transport compound according to claim 1, characterised in that Y is a phenyl group.

A multi-layer photoconductive member for use in electrophotography, comprising: a) a substrate, b) a generation layer, c) a charge transport layer, characterised in that it comprises a polymer according to claim 1 or 2.

A single-layered photoconductive member for use in electrophotography, characterised in that it comprises a charge transport compound according to claim 1 or 2,