Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1998-04-13
2000-09-19
Woodward, Ana
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524459, 524460, 526 79, 526 80, 526201, 526202, C08C 1922
Patent
active
061213640
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/GB96/00980, filed Apr. 24, 1996 which designated the U.S.
The present invention relates to a binder resin, a process for its manufacture and a composition containing it, especially a toner composition for dry development in an image forming process such as electrophotography, electrostatic recording or magnetic recording.
In electrophotography, there is, on the one hand, the need for achieving rapid fixation at as low a temperature as possible. To achieve this, it is necessary for the toner binder to have a relatively low molecular weight. On the other hand, the development process includes contact of the image bearing material with at least one roller, which should not inadvertently remove part of the toner composition due to such contact. In short, the toner must be capable of resisting offset in order to provide improved performance of the toner. In this regard, a relatively high molecular weight polymeric binder is suitable. In an attempt to provide a toner binder which satisfies both of the abovementioned requirements of rapid, low temperature fixing and at the same time resistance to offset, binder compositions having a broad molecular weight distribution, including respective high and low molecular weight polymers, have been employed; see, for example, U.S. Pat. No. 5,219,946.
Such mixtures of high and low molecular weight polymers may be prepared either by preparing a high molecular weight polymer in the presence of a low molecular weight prepolymer or preparing a low molecular weight polymer in the presence of a high molecular weight prepolymer. For example, U.S. Pat. No. 4,486,524 discloses a method of preparing a mixture of high and low molecular weight polymers by suspension polymerisation in which the high molecular weight polymer is first prepared by suspension polymerisation and, in the same polymerisation system, the low molecular weight polymer is then prepared, also by suspension polymerisation. Similarly, EP-A-0199859 discloses the suspension polymerisation of a low molecular weight polymer in the presence of a dispersing agent and in the presence of a prepolymer having a high molecular weight and obtained by emulsion polymerisation. EP-A-0354466 discloses a process for producing a toner resin by a two step suspension polymerisation process in which, firstly, a high molecular weight polymer is produced by suspension polymerisation using specifically an initiator having at least three t-butyl peroxide groups, then secondly, a low molecular weight polymer is prepared using a conventional free radical initiator. After preparation of the high molecular weight polymer, additional monomer, water, dispersing agent and chain transfer agent, for example, may be added if necessary.
In particular, currently, the view tends to be that polymers having a "skewed" molecular weight distribution provide the best toner binders; in particular, they allow the composition to behave as a rubber, i.e. have a tan .delta. approaching unity over a wider temperature range. Such "skewed" polymer compositions preferably contain a relatively large amount of a low molecular weight polymer, a somewhat lower proportion of a polymer of intermediate molecular weight and a small proportion of high molecular weight polymer. The respective molecular weight distribution peaks for each of these respective polymer parts may or may not overlap with one another.
Surprisingly, we have found that polymeric materials are obtainable, using catalytic chain transfer technology, which have a molecular weight distribution particularly suitable for binder resins, especially as toner binder resins for electrophotography but potentially useful for many other surface coating applications such as pressure sensitive adhesives.
Thus, according to a first aspect, the present invention provides a process for the preparation of a polymeric material, which polymeric material comprises at least first and second polymer parts, which first part has a number average molecular weigh
REFERENCES:
patent: 4501845 (1985-02-01), Baus et al.
patent: 4626488 (1986-12-01), Inoue
patent: 5371151 (1994-12-01), Berge et al.
patent: 5391631 (1995-02-01), Baus et al.
De La Motte Anita Margaret
Yeates Stephen George
Woodward Ana
Zeneca Limited
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