Toner for electrophotographic methods and process for preparing the same

Claim 2

A proces for the preparation of monodisperse spherical toner particles having a coofficient of variation below 30 percent and a mean diameter between 2 and 50 μm, which includes the steps of (A) providing monodisperse spherical base particles that have been prepared from (a) an aqueous dispersion of monodisperse seed particles that in addition to a polymer contain a fairly low molecular weight substance which is difficultly soluble in water but which can be absorbed by the polymer, and (b) a monomer which is less difficultly soluble in water than said low moecular weight substance but which can be absorbed in the seed polymer particles containing said fairly low molecular weight substance under conditions permitting molecular diffusion of the monomer to and absorption in the particles, whereafter the monomer in the particles is polymerised, and (B) forming a shell on each of said base particles, such shell forming comprising the steps of (1) adding slowly to the monodisperse spherical base particles a dry polymer powder and a colorant that has been prepared for drying on aqueous dispersion containing finely dispersed polymer particles having a size smaller than one tenth of that of the base particle and a colorant, which drying has been carried out at such a low temperature that the particles do not fuse together, (2) agitating the base particles together with said added dry polymer and colorant until a uniform distribution of the dry polymer and the colorant on the base particles is obtained, (3) fusing the dry polymer to the base particles by melting the dry polymer powder, and (4) repeating at least one of the above steps (1), (2) and (3) until a shell has been formed on the base particles which has a volume between 0.1 and 10 times the volume of the base particles.

Claim 3

A process according to claim 1 wherein the polymer powder forming the shell is prepared from an aqueous dispersion of finely dispersed polymer particles, which particles have been prepared by emulsion or suspension polymerization.

Claim 4

A process according to claim 2 wherein the finely dispersed polymer particles are prepared by emulsifying and homogenising a solution of the polymer, and removing the solvent.

Claim 5

A process according to claim 1 wherein the base particles are kept separated in a continuous gas phase.

Claim 6

A process according to claim 4 wherein the polymer is added in powder form to the base particles and that a temperature is provided which is sufficiently high for allowing adhesion of essentially the entire amount of the shell-polymer to the surface of the base particles and at a temperature which is sufficiently low for preventing any substantial agglomeration mutually between the base particles.

Claim 7

A process according to claim 5, wherein the temperature is increased after the addition of the shell-polymer for sintering the polymer.

Claim 8

A process according to claim 1 wherein a substantial amount of auxiliary particles having a considerably larger size than the base particles, are mixed with the base particles.

Claim 9

Toner particles, essentially consisting of monodisperse spherical particles having a coefficient of variation below 30 percent and a mean diameter between 2 and 50 μm, which monodisperse spherical particles comprise a monodisperse spherical base particle core prepared from an aqueous dispersion of monodisperse seed particles having a mean diamter below about 3 μm, and which seed particles in addition to polymer contains a fairly low molecular substance which is difficultly soluble in water but which can be absorbed by the polymer, by addition of a monomer which is less difficultly soluble in water than the difficultly soluble substance but which can be absorbed in the seed polymer particles containing the difficultly soluble substance under conditions permitting molecular diffusion of the monomer to and absorption in the particles and polymerization of the monomer in the particles, and which monodisperse spherical particles further comprise a shell on the base particles prepared by adding slowly, continuously or stepwise, to the polymerized monodisperse spherical base particles, a polymer powder and a colorant, prepared from an aqueous dispersion containing finely dispersed polymer particles, of a size smaller than one tenth of that of the base particle, and colorant, which dispersion has been dried at such a low temperature that the particles do not fuse together, agitating the base particles together with the added polymer and colorant until a uniform distribution of the polymer and the colorant on the base particles is obtained, fusing the polymer to the base particles by melting of the dry polymer powder and repeating one or more of the above steps until a shell has beenformed on the base particles of a volume between 0.1 and 10 times the volume of the base particles.

Claim 10

Toner particles, essentially consisting of monodisperse spherical particles having a coefficient of variation below 30 percent and a mean diameter between 2 and 50 μm, which monodisperse spherical particles comprise a monodisperse spherical base particle core prepared from an aqueous dispersion of monodisperse seed particles having a mean diamter below about 3 μm, and which seed particles in addition to polymer contains a fairly low molecular substance which is difficultly soluble in water but which can be absorbed by the polymer, by addition of a monomer which is less difficultly soluble in water than the difficultly soluble substance but which can be absorbed in the seed polymer particles containing the difficultly soluble substance under conditions permitting molecular diffusion of the monomer to and absorption in the particles and polymerization of the monomer in the particles, and which monodisperse spherical particles further comprise a shell on the base particles prepared by adding slowly, continuously or stepwise, to the polymerized monodisperse spherical base particles, a polymer powder and a colorant, prepared from an aqueous dispersion containing finely dispersed polymer particles, of a size smaller than one tenth of that of the base particle, and colorant, which dispersion has been dried at such a low temperature that the particles do not fuse together, agitating the base particles together with the added polymer and colorant until a uniform distribution of the polymer and the colorant on the base particles is obtained, fusing the polymer to the base particles by melting of the dry polymer powder and repeating one or more of the above steps until a shell has beenformed on the base particles of a volume between 0.1 and 10 times the volume of the base particles.

Claim 11

Toner according to claim 8, in which the ratio of shell volume to core volume is between 0.5 and 5.

Claim 12

Toner according to claim 8 in which the ratio of shell volume to core volume is between 0.2 and 1.

Claim 13

Toner according to claim 8 in which the colorant is a pigment and is present in the shell in an amount between 5 and 40 percent by volume.

Claim 14

Toner according to claim 8 in which the particles comprise an uncolored shell on top of the shell containing a colorant.