Process for the preparation of toner particles

Description

[0001] The present invention relates to a process for the preparation of toner particles under high deformation by dispersing a resin in a liquid carrier. The invention also relates to a toner composition and a developer composition comprising the particles obtained with said process.

[0002] Toner particles are used in electrophotographic processes. Electrophotographic processes are described in, for example, US-A-2297691. In these processes, a photoconducting insulating layer is first given a uniform electrostatic charge over its surface, then selectively exposed to light to dissipate the charge in the illuminated areas, thereby forming an electrostatic latent image. The electrostatic latent image may be developed by adhering charged powder, called toner, to the electrostatic latent image, thereby making the latent image visible. This visible image can be applied to a substrate, like paper, by transferring the powder to the substrate, and can be permanently fixed to this substrate.

[0003] A process for the preparation of resin toner particles under high deformation by dispersing a resin in a liquid carrier is described in US-A-3910846. In this process, a fluid polyester with an acid content of about 0,02 milliequivalents to about 1,5 milliequivalents per gram of polyester is admixed with an aqueous basic solution under relatively high deformation conditions, being high shear, thereby forming an emulsion, which is subsequently dried. To form the desired emulsion, a large amount of energy is required, which can be supplied by conventional emulsification equipment with high power ratings, like for example simple mixers, colloid mills and homogenizers.

[0004] A major drawback of the process according to US-A-3910846 is that the process is a batch process, in which a limited deformation may be applied. Because of this limited deformation, there is a restriction to the viscosity of the resins which can be processed in this process. Another disadvantage of this process is the high expenditure of energy.

[0005] It is the object of the present invention to provide a process for the preparation of toner particles under high deformation by dispersing a resin in a liquid carrier, which process is not a batch process, in which process there is no limitation to the viscosity of the resin and in which process there is no need for high amounts of energy.

[0006] These objects are achieved by producing toner particles by a process in which a resin is mixed with toner additives and a liquid carrier under extrusion conditions, in which a dispersion of toner particles in the liquid carrier is formed, and in which the toner particles are allowed to dry.

[0007] It is an advantage of the process according to the invention that the heating, the mixing and the dispersion of the resin, the toner additives and the liquid carrier may be performed rapidly in the same device.

[0008] The extrusion conditions include a temperature ranging between 15°C and 300°C, a pressure ranging between atmospheric pressures and 70 bar (70.10⁵ Pa), and a solids content up to 65%. According to a preferred embodiment of the invention the extrusion temperature is between 80°C and 150°C.

[0009] Preferably, the process according to the invention is a continuous process.

[0010] According to a further preferred process according to the invention, the continuous process is carried out in an extruder or in a continuous kneader. Most preferably the process is carried out in an extruder. Suitable extruders include for example an intermeshing or non-intermeshing co- or counter-rotating twin screw extruder, single screw extruder, Drais stator-rotor extruder or a co-rotating multi-screw extruder.

[0011] Preferably an intermeshing co-rotating twin screw extruder is used.

[0012] Suitable kneaders include for example a Buss Ko-Kneter or a Farrell continuous Banburry mixer.

[0013] The use of an extruder in a continuous process provides the advantage of an improved control over the process parameters so that the properties of the resin dispersion can be optimised.

[0014] Due to the process according to the present invention, the dispersion may be processed at a temperature higher than 100°C, by adjustment of the pressures, which is not possible for the prior art processes.

[0015] Furthermore, it is also possible to process highly viscous, and viscoelastic resins without the need for the presence of organic solvents during the process. The dynamic viscosity of these resins may be between 0,1 and 1000000 Pas (measured at 120°C, at an angular frequency of 1 rad/sec).

[0016] Preferably, the dynamic viscosity of these resins is between 10 and 100000 Pas.

[0017] Another advantage of the process according to the invention is that the particle size and the shape of the obtained toner particles may be directed.

[0018] The shape of the particles may be modified by processing the drying step by different methods.

[0019] In case the drying is performed in the extruder by flashing, the toner particles will coagulate, and will become irregularly shaped. With the term flashing is meant the expansion of a closed system at processing temperature and corresponding high pressure as described above, by releasing the pressure to atmospheric pressure.

[0020] The irregurarly shaped toner particles are particularly suited to be used in dual component development.

[0021] In case the toner particles are dried by spray-drying, the toner particles retain there spherical shape. These particles are particularly used in mono component development.

[0022] Generally, the particle size of the toner particles is between 0,1 and 15 µm. Preferably, the particle size is between 3 and 7 µm.

[0023] The term 'particle size' as used herein, means volume weighted diameter as measured by conventional diameter measuring devices, such as for example a Coulter LS 230, sold by Berkman Coulter, Inc.. The term 'volume weighted diameter' is the sum of the mass of each particle times the diameter of a spherical particle of equal mass and density, divided by total particle mass.

[0024] Another advantage of the process according to the invention is that the toner particles are formed in the emulsification step. Consequently there is no need for a grinding and a classification step.

[0025] In a further preferred process according to the present invention, the resin and the toner additives are subjected to a pre-mixing step under extrusion conditions to form a molten mixture. This mixture is subsequently dispersed in the liquid carrier in which particles are formed. An advantage of this pre-mixing step is an improved homogenisation of the additives.

[0026] Toner additives include for example surfactants, colorants, charge control agents, waxes and flow agents.

[0027] In colour toner compositions, the colour strength is improved by the use of the pre-mixing step.

[0028] Suitable examples of resins to be used in the process according to the present invention include polyesters, polyamides, polyolefins, styrene (meth)acrylates, styrene butadienes, crosslinked styrene polymers, epoxies, polyurethanes, vinyl resins and/or polyester imides.

[0029] Preferably, the resin is a polyester and/or a styrene acrylate.

[0030] The polyester may be acid, hydroxyl, epoxy or phosphoric acid functional.

[0031] The acid number of an acid functional polyester containing carboxylic acid is preferably higher than 10, and preferably higher than 15. The acid number is preferably lower than 60 and less than 35.

[0032] The Tg of the polyester may be greater than 45°C, and is preferably greater than 60°C. The Tg is generally lower than 90°C.

[0033] The liquid carrier for the dispersion of the present invention is chosen depending on the temperature and the pressure of the process. This carrier is immiscible with the used resin and is chosen from for example water, liquid hydrocarbons, for example a liquid alkane, an oil. Suitable alkanes include for example hexane, heptane, octane, and a high boiling alkane, such as for example nonane, decane, dodecane and isohexadecane. Preferably, the liquid carrier is water.

[0034] The stability of the composition may be improved by incorporation of a surfactant, such as for example an ionic or a non-ionic surfactant. Examples of useful ionic surfactants are sodium alkylaryl sulfates, sodium lauryl sulfate, sodium alkyl naphthalene sulfonate, the sodium salt of alkylaryl polyether sulfonate, dioctyl sodium sulfo succinate, and the like. Examples of useful non-ionic surfactants are polyoxyethylene-polyoxypropylene block polymers, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, sorbitan monostearate, and the like. Also blends of ionic and non-ionic surfactants can be used, like for example polyoxyethylene sorbitan esters of fatty resin acids and alkyl sulfonates and the like.

[0035] Suitable colorants, dyes or pigments which are added to the toner composition to impart color to the developed images, include for example, carbon black or red, blue, green, brown, magenta, cyan and yellow pigment particles, and mixtures thereof.

[0036] It is preferred to add these colored pigment particles to the composition before the pre-mixing step, in order to obtain better dispersed pigment particles in the resin. The pigment particles may be present in amounts of between for example about 1 wt% to about 20 wt%, and preferably between about 2 wt% to about 10 wt% based on the amount of the resin.

[0037] Suitable charge control agents include for example a positive-charge control agent or negative-charge control agent. Examples of the positive-charge control agent include nigrosine dyes , triphenylmethane dyes, containing a tertiary amine as a pendant group, quaternary ammonium salt compounds, cetyltrimethylammonium bromide, polyamine resins, imidazole derivatives. Examples of the negative-charge control agent include metal-containing azo dyes; copper phthalocyanine dyes, metal complexes of salicylic alkyl derivatives and quaternary ammonium salts.

[0038] The charge control agent may be incorporated in the toner composition in an amount between for example 0.1 wt% and 8.0 wt% and preferably between 0.2 wt% and 5.0 wt%, based on the amount of the resin.

[0039] In the toner compositions waxes can be present, as internal release agents, like for example waxes with a molecular weight (Mn) of from about 1000 to about 10000, such as for example polyethylene or polypropylene, hydroxy alcohols and paraffin waxes. These waxes usually are present in amounts of 0,5 wt% to 5 wt% based on the amount of the resin.

[0040] To the dry toner particles obtained with the process according to the invention powder flow particles, like for example silicates and microtalc may be added.

[0041] The process according to the invention will be illustrated by the following example, which is only intended to illustrate and not limit the scope of the invention.

Example I

[0042] In this example the co-rotating twin-screw extruder ZSK-30 (Werner & Pfleiderer) was used with the following screw configuration : 7 right-handed conveying elements, 3 right-handed kneading elements, 2 left-handed conveying elements and 20 neutral kneading elements (in which 11 right-handed conveying elements are equally divided).

[0043] 45 wt% solid resin (Uralac P2400™ of DSM Resins), was dosed with 5 wt% surfactant, a polyoxyethylene-polyoxypropylene block polymer, (Poloxamer 338) on the first extruder element. Next, 50 wt% water was injected on 3 points, divided equally on the neutral kneading elements. The temperature of the first 7 right-handed conveying elements was kept on 20°C, the next 3 right-handed kneading elements, 2 left-handed conveying elements and 3 neutral kneading elements were kept on 60°C. The rest of the extruder-elements were kept on 90°C.

[0044] The resin was dosed at 5.4 kg/h. and the surfactant at 0.6 kg/h. The first and second water-injection point was set at 1.5 kg/h, the third water-injection point was set at 3 kg/h., so the total extruder throughput was 12 kg/h.

[0045] The particle size of the resin in water, stabilised by the surfactant, measured by a Coulter LS 230, was 6.4 µm.

Claims

1. A process for the preparation of toner particles under high deformation by dispersing a resin in a liquid carrier, characterised in that a resin is mixed with toner additives and a liquid carrier under extrusion conditions, that a dispersion of toner particles in the liquid carrier is formed, and that the toner particles are allowed to dry.

2. A process according to Claim 1, characterised in that the steps of mixing the resin and the toner additives in the liquid carrier and dispersing of the toner particles in the liquid carrier are carried out sequentially in a continuous process.

3. A process according to any one of Claims 1-2, characterised in that the mixing and dispersing steps are carried out in an extruder.

4. A process according to Claim 3, characterised in that the extruder is an intermeshing co-rotating twin screw extruder.

5. A process according to any one of Claims 1-4, characterised in that the liquid carrier is immiscible with the toner particles.

6. A process according to Claim 5, characterised in that the liquid carrier is water.

7. A process according to any one of Claims 1-6, characterised in that the resin is a polyester resin and/or a styrene acrylate resin.

8. A process according to any one of Claims 1-7, characterised in that the dried toner particles have a particle size of 0,1-15 µm.

9. A toner composition comprising toner particles obtained by a process according to any one of Claims 1-8.

10. A developer composition comprising toner particles obtained by a process according to any one of Claims 1-8.