Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1988-10-26
1990-05-08
Goodrow, John L.
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430137, G03G 900, G03G 1306
Patent
active
049237764
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to toner particles for use in electrophotograhic copying or electrostatic printing. More particularly the invention relates to such toner particles having a pimply surface. The invention also relates to methods for the preparation of such toner particles.
In electrophotographic copying the latent print on the photo-drum is developed with a toner consisting of fine-grained pigmented thermoplastic particles. The most common method of preparing a toner comprises melting a thermoplastic material and mixing this with pigment, charge modifiers, release agents etc. The product is then cooled, crushed, ground and screened in an air stream to obtain particles with a size in the order of from 5 to 30 .mu.m. According to this method particles of very varying shapes and sizes are obtained. This variation in shape and size gives rise to certain disadvantages in the copying process. Efforts have thus been made to find processes which give toner materials having spherical and fairly uniformly sized particles.
One way of preparing a toner is to finely divide molten waxes or low molecular thermoplastic materials in a spray drier. If such conditions are used at the spray drying that a suitable particle size is obtained directly the grinding step can hereby be eliminated. A disadvantage of the spray drying is, however that the size distribution of the powder is fairly wide. Further, it is not possible to satisfactorily spray dry a melt of the thermoplastic materials which are usually used at so-called heat fixing by means of hot rolls or radiation. Spray dried powders are more suitable as toners intended for cold fixing by means of pressing. Spray dried particles are advantageous in that they are spherical and thus not of such varying shapes as ground particles.
One method of preparing toner particles suitable for hot fixing, which method in principle is very cheap, is to disperse pigments, charge modifiers, release agents, initiators etc in monomers which give polymers having suitable properties for heat fixing. The monomer is emulsified with a suitable colloid system in water, the temperature is raised and by polymerization a fine, pigmented powder of sperical particles is directly obtained and this powder can be dried, after washing, to give a powder suitable for use in coping. Since the method is very simple several attempts have been made to prepare toner particles in this way. One process of this kind is disclosed in the British patent application 2091435. In practical tests it has been found that particles prepared by suspension polymerization have certain advantages such as the capability of giving copies with good resolution. However, it has also been found that such particles have a serious disadvantage in that they have such a strong adhesion to the photo-drum that they are only very incompletely transferred to the paper. Such particles also agglomerate strongly with each other which means that such a toner has very poor free-flowing properties etc.
The drawbacks with the particles mentioned above can be related to the smooth surface of the spherical particles prepared by normal suspension polymerization. When spherical particles with a smooth surface are used the adhesion to the photo-drum will be so strong that they are not even completely removed at the cleaning of the photo-drum which follows the transfer step. Such remaining toner thus leads to a rapid deterioration of the quality of the copies. A strong adhesion to the photo-drum is particularly serious if the toner consists of or contains very fine particles, <5 .mu.m, since it is more difficult to remove such fine particles from the surface of the photo-drum by means of mechanical cleaning systems.
According to the present invention it has been found that spherical particles having a pimply surface do not show the disadvantage of a strong adhesion to the photo-drum. In several cases such particles even have lower adhesion than toner particles prepared by the conventional grinding process.
The present invention thus relates
REFERENCES:
patent: 4254203 (1979-11-01), Oka et al.
patent: 4254204 (1981-03-01), Kato et al.
patent: 4614698 (1983-07-01), Miyakawa et al.
patent: 4670368 (1983-06-01), Tosaka et al.
patent: 4794065 (1988-12-01), Hedvall et al.
Patent Abstract of Japan, vol. 7, No. 60, P-182, Abstract of JP 57-207259, publ. 1982-12-18.
Hedvall Bertil
Mattson Gunnar
Porrvik Sten
Sundstrom Goran
Casco Nobel AB
Goodrow John L.
Philpitt Fred
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