Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-11-28
2003-11-25
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C585S443000, C564S433000, C430S058700
Reexamination Certificate
active
06653510
ABSTRACT:
The present invention relates to certain polymeric materials, and compositions containing them which are charge transport materials. The invention also relates to processes for making these polymers and their use in devices such as electroreprographic devices and electroluminescent devices.
Polymers of the invention may be used in the field of electroreprography. Electroreprography is any process in which an image is reproduced by means of electricity and incident radiation, usually electromagnetic radiation, more usually visible light. Electroreprography includes the technology of electrophotography which encompasses photocopying and laser printing technologies. Typically, in both a photocopier and a laser printer, a photo-conductive member is first charged in the dark (e.g. by applying a high voltage via a Corona discharge). Then a latent electrostatic image in charge is produced by partial exposure of the charged photo-conductive member (e.g. a drum or belt) to radiation (e.g. light). The radiation neutralises the charge in the exposed regions. The light source can either be reflected light from an illuminated image (photocopying) or from a laser which scans the photo-conductive member usually under instruction from a computer (laser printing). Once a latent image has been produced in charge, it is developed with toner, the toner is transferred onto a substrate (e.g. paper) and then fixed thereto (e.g. by heat) so that a visible image is obtained.
The photo-conductive member typically comprises a photo-conductor (e.g. an organic photo-conductor [“OPC”]) which must perform two different functions: generate a charge on exposure to the incident radiation; and transport the photo-generated charge to the surface. The unexposed regions of the photo-conductive member will retain their charge and form the latent image. It is usual to use different materials for each of these two processes and develop materials which are separately optimised for their ability to generate photo-induced charge (charge generating materials or “CGMs”) or their ability to transport charge (charge transport materials or “CTMs”). The photo-conductor can be constructed as a single layer or from a plurality of layers, for example from at least one charge generating layer (“CGL”) comprising the CGM and at least one separate charge transport layer (“CTL”) comprising the CTM.
An ideal photoconductor would be one where the material charges rapidly to a high value in the dark, retains the charge in the dark (i.e. exhibits no dark decay) and shows rapid total discharge on exposure to low-intensity illumination. The time taken for the charge-discharge cycle of a photo-conductor limits the maximum speed at which the latent image can be generated. Photo-conductive materials with improved electrical properties may allow faster printing and copying and/or higher quality copies and/or longer component life.
The applicant has discovered means to improve the charge transport properties of certain polymers based on triaryl amine repeat unit(s).
PCT/GB98/03685 is a co-pending patent application which describes novel CTM polymers of repeat unit of Formula D
where Y
1
is N, P, S, As and/or Se and Ar
1
, Ar
2
and Ar
3
are aromatic groups. These polymers are prepared by the addition of an end capping reagent to control the molecular weight of the final polymer and hence its desirable properties as a CTM.
The disclosure of this co-pending application is incorporated herein by reference; its definitions and description should be used in connection with the present invention except as modified herein.
The procedure of the co-pending application produces attractive charge transfer agents. However we have now found that they may be further improved and indeed similar-materials which are not end capped may be improved by isolating an appropriate molecular weight fraction from them. We have found that medium molecular weight. polymers are generally superior to lower and higher molecular weight polymers derived from the same starting materials; lower molecular weight polymers are less effective and crystallise more readily and are thus not durable; higher molecular weight polymers are durable but less effective. By means of this invention a fraction may be selected which is of good performance and is sufficiently durable to cover the required life of components of electroreprographic devices whilst optimising its charge transport effectiveness.
According to one aspect of the present invention there is provided a process which comprises isolating, from a polymer comprising repeating units which are individually of Formula X
in which
Y is P or N,
Ar
1
& Ar
2
are bivalent aromatic groups,
Ar
3
is a monovalent aromatic group, and
the units of Formula X may be the same or different,
a molecular weight fraction which is a charge transport material.
According to a another aspect of the present invention there is provided a process in which an improved charge transport material is produced by isolating, from a first charge transport material which is a polymer comprising repeating units which are individually of Formula X
in which
Y, Ar
1
, Ar
2
and Ar
3
are as previously defined; and
the units X may be the same or different,
a molecular weight fraction of improved charge transport properties.
Ar
1
Ar
2
and Ar
3
preferably comprise benzenoid rings which are optionally fused with other, preferably benzenoid, rings and/or substituted.
The polymer may be a block copolymer comprising such repeat units.
Trivalent repeat units of Formula D may be included to permit a degree of chain branching if desired.
The molecular weight fraction produced by the process according to the present invention may be of Formula 1:
AX
m
B Formula 1
in which
each X is a unit of Formula X as defined above and may be the same or different;
A and B are chain terminating groups, for example, hydrogen, chlorine, bromine or iodine, or other leaving groups used in a polymerisation process by which the polymer is made, or end capping groups, and
m is the average number of X units per molecule of the fraction.
The value of m is suitably 4 to 50, preferably 4 to 30, more preferably 4 to 25 for example 4 to 15 and especially 5 to 13 or 6 to 14. Generally it is desired that m is at least 5 in all of the above ranges.
The polydispersity of the fraction is suitably 1.1 to 4, preferably 1.1 to 3 and more preferably 1.2 to 2.5. Suitably the fraction is substantially free from molecules having 3 or fewer or 50 or more repeat units.
The aryl groups may be mono- or poly-cyclic and the rings are preferably benzene rings substituted with, for example, one or more C
1-40
-alkyl groups in order to increase their solubility in for example tetrahydrofuran (THF) for processing purposes. They may have fused ring groups, naphthyl groups or covalently linked benzene rings for example biphenyl residues but are preferably benzene rings which are each substituted with alkyl groups providing a total of one to eight aliphatic carbon atoms per benzene ring.
Preferably the groups A and B are inert to coupling with further molecules of the polymer so as to reduce the likelihood of further growth of molecules to undesired sizes. Thus it is preferred that they should not be halide atoms.
Molecular weight fractions produced by the present invention may be isolated from polymers prepared without the addition of a separate end capping reagent to control the molecular weight of the polymer.
Isolation of the molecular weight fraction may be by filtration technologies, chromatographic techniques, osmotic methods, and/or solid extraction using a suitable solvent, for example Soxhlet extraction.
In a preferred form of the invention (which may be used together with one or more of the above techniques) the process comprises a step of partially precipitating from a solution of the polymer in a suitable solvent, a molecular weight fraction thereof. It may be separated by dissolving the polymer in the solvent, precipitating a least soluble (highest molecular weight) fraction and then r
Allen Joanne Victoria
Brown Beverley Anne
Leeming Stephen William
Morgan John Dylan
Veres Janos
Avecia Limited
Barts Samuel
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