Polyesters based on hydroxyl-containing prepolymers of olefinica

Details Polyesters based on hydroxyl-containing prepolymers of olefinica Polyesters based on hydroxyl-containing prepolymers of olefinica

1994-09-30

1996-02-27

Acquah, Samuel A.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Ethylenically unsaturated reactant admixed with either...

528176, 528179, 528189, 528192, 528194, 528205, 528219, 528272, 528288, 528302, 528306, 5283086, 525165, 525178, 525179, 525420, 525425, 525437, 525438, 525445, 430109, C08G 6348, G03G 900

Patent

active

054949645

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to novel polyester resins based on hydroxyl-containing prepolymers of olefinically unsaturated monomers and their use as binders for electrophotographic toners. The present invention furthermore relates to electrophotographic toners containing these polyester resins as binders.
Electrophotographic toners have to meet a large number of requirements which arise from the copying process, toner production or the handling of the toners. Many of the requirements which a toner has to meet are determined by the binder, ie. by the toner resin.
Thus, a toner resin must be capable, for example, of readily dispersing additives such as carbon black, ferrites, magnetite, Aerosil, charge stabilizers and waxes. Homogeneous dispersing is necessary since otherwise toner particles having very different electrostatic properties may be present.
Another requirement is good millability of the toner resin. In toner production, reverse-jet mills are generally used. Some resins give toners which require very long times before they can be brought to the desired particle size, preferably from 5 to 15 .mu.m, in a reverse-jet mill. Another frequent problem in milling in the reverse-jet mill is the production of fine dust, ie. of particles which have a particle size which is less than 5 .mu.m.
The shelf life of a toner is also influenced by the toner resin. A resin which becomes soft at room temperature or at the temperatures prevailing in the copier and can stick together gives toner powders which can cake and are no longer free-flowing. Caking of the toner powder may also occur if a moisture-sensitive resin which is even only slightly hygroscopic is used. In addition, resins which absorb moisture from the surrounding air lead to toners whose electrostatic properties are greatly dependent on the atmospheric humidity. The consequences are the occurrence of background and irregular blackening in solid areas on the copy.
A further problem is the increase in the fixing rate of an image transferred to the print medium (acceptor) by heat, ie. the increase in the cycle time of the copier. The properties of a toner during fixing are greatly influenced by the melting behavior of the toner resin. A higher fixing rate is achieved by using a resin having a low softening point. However, this may result in the problem of hot offset, ie. some of the molten toner remains adhering to the hot fixing roller of the copier and is transferred to subsequent copies.
In U.S. Application No. 4,657,837 (1), the problem of hot offset is solved by using a branched polyester of terephthalic acid, trimellitic acid and ethoxylated or propoxylated bisphenol A. Toners consisting of this resin have very good anti-offset properties but, owing to their high softening point, are unsuitable for copiers having cycle times of more than 50 copies per minute, since adequate fixing on the print medium (acceptor) is not achieved.
Polyesters having a lower softening point but poorer anti-offset properties are described in U.S. Aapplication No. 4,980,448 (2). These polyesters are obtainable by reacting a dicarboxylic acid component, a diol component and a crosslinking agent. However, in the preparation of these resins there is a danger that excessive crosslinking may occur in the polycondensation.
EP-195 604 (3) discloses polyesters for use in toner mixtures, which are obtainable by copoly-condensation of a diol component of ethoxylated or propoxylated bisphenol A with a copolymer of styrene or a styrene derivative and a carboxyl-containing vinyl monomer. These polyesters, too, do not solve the prior art problems described.
Toner resins which have a very high viscosity after melting or which melt only very slowly exhibit the phenomenon of cold offset, ie. toner particles are not correctly fixed on the paper and may therefore remain adhering to the fixing rollers. The literature frequently describes the use of resins having a bimodal molecular weight distribution, which avoid cold and hot offset. This can also be achieved by using resin mixtures or resi

REFERENCES:
patent: 4657837 (1987-04-01), Morita et al.
patent: 4980448 (1990-12-01), Tajiri et al.

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