JP2000053781A - Round polymer particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain in high cost efficiency rounded thermoplastic particles useful as polymeric powdery particles, in particular dry toner used in electrostatic printing and copying technique by mixing thermoplastic particles with non- thermoplastic particles followed by cooling. SOLUTION: The rounded thermoplastic particles is obtained by the following procedure: (A) thermoplastic particles having a volume-average diameter dv50 and plasticizing temperature Tplast is mixed with (B) non-thermoplastic particles having such a volume-average size d2v50 as to meet the relationship: d2v50>=1.5×dv50 and specific gravity >=1.5 times that of the particles A, the resulting mixture is mechanically agitated for 5 min or longer at such a temperature Tmix as to meet the relationship: Tplast-15 deg.C<=Tmix<Tplast+30 deg.C to effect rounding the thermoplastic particles, and the mixture is cooled and the objective rounded thermoplastic particles are recovered from the mixture; wherein the component B to be used is pref. inorganic particles or beads, and the particles A is mixed at 3-15 pts.wt. with 100 pts.wt. of the particles B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for rolling and / or coating polymer particles. Specifically, but not exclusively, the rounding of the polymeric toner particles and / or
Or a method for coating.

[0002]

BACKGROUND OF THE INVENTION In recent years, there has been increasing interest in powders, especially in applications intended to produce thin multifunctional layers on a substrate. Such applications can be aimed at a uniform layer or can be aimed at producing an image-like pattern. The particular method used to achieve such a layer can be of various types, for example, electrostatic powder spray coating, dipping, etc. or of images starting from electroscopic powder particles. More complex methods such as electrophotography for formation can be used, the latter particles then usually being dry toner particles.
les). In all applications, smaller particles need to be sought to improve the coating in terms of quality, such as smoothness, but also to reduce material costs. However, one of the major problems encountered when seeking smaller dimensions in powders is the increase in the specific surface area of such powders, which greatly increases the cohesion and thus the propensity for agglomeration. This results in the presence of relatively large particles that are the agglomerates during the coating process,
Thus, the benefit of using smaller particles is at stake.
In most cases this limits the use of smaller particles,
Thus hindering further advances in technology towards improved and cheaper thin layers. The actual detailed control of the shape of the particles may also be relevant, with some potatoes being
There is evidence that a similar structure is interesting.

[0003] A number of methods have been proposed to address this problem in that spherical or hemi-spherical particles are used to increase resistance to agglomeration. Another proposed solution to the problem is the design of core-shell particles with special low energy surfaces to minimize cohesion and agglomeration forces. While these proposals actually reduce the problem of agglomeration of toner particles, the use of these concepts has led to the production of such rounded and / or surface-designed particles with little and no margin. It is very limited by the fact that there are only complex methods. Several methods have been proposed for the production of the particles. Whether there is some room for control of the potato-shaped or not depends on the method.

[0004] In the first method, particles are produced directly from suspension polymerization. Some related methods have been proposed to disperse the particles from the binder solution by dispersing it in an incompatible liquid and subsequently evaporating the solvent used in the dispersion droplets to reveal solid particles. To manufacture.

[0005] In yet another proposed method, homo-,
Pre-particles using hetero- and / or thermal assisted and / or flocculant assisted methods
s), producing the particles in situ, for example by flocculation of the latex particles. Yet another proposed method involves dispersing solid particles and in most cases the Tg of the particles.
Heating above its corresponding plasticizing temperature allows stirring to take on a more spherical shape. Such a method is US
-A-4 345 015, in which irregularly shaped particles are placed under stirring in a liquid carrier and heated to a temperature at which the resin particles soften until they become spherical. Is disclosed.

[0006] In all of the cases, the particles are present in the liquid for some time and must be removed, discarded and the particles dried, in which case the powder particles are subsequently applied in a coating process. Care must be taken to ensure that there is no dry residue on the surface, such as when electrostatic methods are used, to avoid hydrophilicity on the particles. The use of energy for drying and the problems encountered to avoid agglomeration during drying must also be overcome. These problems significantly reduce the usefulness of these methods.

[0007] In a second method, the particles are produced by using a stream of hot gas. In a first proposed method, non-spherical particles are continuously injected and supplied into a heated gas stream. The temperature and residence time in the process are chosen in such a way that the particles are allowed to take a more spherical shape. Preferably, the temperature is set to a temperature above the plasticization temperature of the polymer contained in the particles to be rounded particles, i.e. above the Tg. The method can be performed as a batch method or as a continuous method. This is known in the art as fluidization.
zation). In yet another method, a dispersion of particles in a liquid is made and subsequently spray dried.
In that particular case, evaporation of the dispersant must take place, and the amount of energy must be sufficient to plasticize the particles. In yet another method, the particles are dissolved and / or dissolved / partially dispersed in a liquid, spray dried and the solvent /
Remove the dispersant. During evaporation of the solvent, the particles are dried and shaped to form spherical particles. A disadvantage of all of the above embodiments of the second method is that a large amount of hot gas and thus also a large amount of energy is required, since the sphering process can only be carried out at temperatures above the plasticizing temperature. Another disadvantage is that this method has a tendency to form agglomerates and contamination of the equipment walls during the process.
To avoid these drawbacks, one must work at a low particle / gas ratio, resulting in a low throughput of rounded particles and the use of large amounts of heated gas, which makes this method an economically problematic one. There is a certain way. Yet another significant problem is that finely divided powders are made in gas, which, in the presence of oxygen, produce powder explosions (powder ex).
loss). An inert atmosphere must be used to reduce the risk, which is very expensive in such large volumes. Yet another disadvantage is that at the end of the process, the particles and the heated gas must be separated. This implies special precautions for cooling the gas, which means that measures must be taken to control fines in the final "clean" gas stream, which is again costly.

In a third method, described in US Pat. No. 4,915,987, the particles are placed in a mechanical mixing device where the particles are rolled by applying mechanical and / or thermal energy. To form particles. The temperature regulation of this method is crucial. Agglomeration of the particles and contamination of the inner walls of the device with the plasticized material can easily occur. This requires an additional sieving step to obtain the initial particle size. The temperature control is also difficult because the particles are in a fluidized state and this control also requires the use of complicated and expensive cooling equipment.
To avoid agglomeration, the particle concentration is kept low, thus resulting in a low production rate, since the batch method is self-evident in such an apparatus. This also increases the cost of the particles produced by the method. Degradation can also occur due to wear due to high mechanical impact on the particles of the mixing device rotor, which requires an additional separation step to remove fines generated during the rolling process. Means to get. Therefore, these methods also have disadvantages.

From the above method, we can learn that there is still a need for improvements in methods for rounding the particles and for allowing a core-shell design on the powder particles.

[0010]

OBJECTS AND SUMMARY OF THE INVENTION A first object of the present invention is to provide a simple and cost effective method for rounding polymer powder particles, especially dry toner particles for use in electrostatic printing or copying processes. It is to be.

A second object of the present invention is to provide a simple and cost-effective method for coating polymer particles while simultaneously rolling them.

A first method according to the invention comprises: mixing thermoplastic particles having an average volume diameter d _v50 and T _plast with “non-thermoplastic” particles, the latter being d2 _v50 ≧
1.5Xd _v50 has a volume average particle size d2 _v50 and at least 1.5 times larger specific gravity than the particles of the specific gravity should be rounded such that, - the mixture at least 5 minutes, T _plast -15 ℃ ≦ T
mechanically mixing at a temperature T _mix such that _mix <T _plast + 30 ° C., rounding the thermoplastic particles, cooling the mixture, and recovering the rounded thermoplastic particles from the mixture. This is achieved by providing a method for rolling thermoplastic particles comprising the same.

A second method of the present invention comprises: _mixing thermoplastic particles having a mean volume diameter d _v50 and T _plast with a polymeric coating material and “non-thermoplastic” particles, the latter having d2 _v50 ≧ 1. 5xd the volume average particle size d2 such that _{v50 v50} and has at least 1.5 times larger specific gravity than the specific gravity of the thermoplastic particles, - the mixture at least 5 minutes, T _plast -15 ℃ ≦ T
mechanical mixing at a temperature T _mix such that _mix <T _plast + 30 ° C., coating the thermoplastic particles, cooling the mixture, and recovering the thermoplastic particles from the mixture. This is achieved by providing a method for coating plastic particles.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing thermoplastic particles, especially dry toner particles, such as melt-kneading and subsequent cooling, which produces particles having surfaces with very irregular shapes and irregularities. It relates to the rounding of thermoplastic particles produced by grinding the toner mass and separating the particles. In FIG. 1, the picture labeled quality D shows such particles. This time, such thermoplastic particles, especially dry toner particles, can be rolled by a simple, quick and cost-effective mechanical method, i.e., after processing, the particles have a somewhat round shape and a surface with almost no bumps Is found. In fact, after treatment according to the method of the invention, the particles have a potato-like shape with a rather smooth surface.
In FIG. 1, the photograph labeled quality A shows the particles after treatment using the method of the present invention.

The method of the present invention is basically a method of agitating thermoplastic particles together with particles having a specific gravity larger than that of the toner particles and higher than that of the toner particles at a temperature near the plasticizing temperature T _plast .

The plasticizing behavior of most thermoplastic materials is T
The g-behaviour can be described. In such a case, the temperature _Tplast will be Tg. The tests used to determine the Tg for simple materials are as simple as the DSC- (differential scanning calorimeter) method.

For more complex material or resin mixtures
If T_plastIs limited by testing for deformability
Should. In this document, the material was weighed at 40 kg at various temperatures.
/ Cm ^TwoBy subjecting to a load of 10 minutes, complex materials
Fee T_plastTo determine. 10% permanent deformation (perm
anent deformation) is found
Temperature T_plastAdopted at ° C. Basically, a single tree
T determined as above for fat_plastIs T
4 to 6 from g^oGive a low temperature.

The temperature of the rounding process depends on another heating and / or
Or it can be set by the mixing method itself, which can deliver enough heat in a start-up mode to heat the mixture by friction. In each case, the temperature during mixing was T _plast -15 ° C.
≦ T _mix <T _plast + 30 ° C., preferably the rounding temperature is T _plast −10 ° C. ≦ T _mix <T
_{Adjusted to be plast} + 30 ° C. In a very preferred embodiment, the rounding temperature is T _plast ≦ T _mix <T
_{Adjusted to be plast} + 30 ° C. The upper limit for T _mix depends at least in part on the magnitude at which the rounding of the present invention is performed. Relatively small, eg up to about 1
When rounding with a mixer having a volume of 0 liters, T
There is not much need to use a T _mix higher than _plast + 10 ° C, and when rolling on a medium scale, eg, a mixer having a volume of 10 to about 50 liters, there is no need to use a T _mix higher than T _plast + 20 ° C. _{Alternatively} , for larger scale rounding, it is beneficial to use a T _mix close to T _palst + 30 ° C.

The preferred types of so-called "other" particles used for the process disclosed above are crosslinked and / or
Or the use of "non-thermoplastic" particles selected from the group consisting of highly filled resin particles and inorganic particles.
Preferably, inorganic particles or beads are used. Preferably, smooth spherical particles are used. d2 _v50 ≧ 1.5x
It is preferred to use “non-thermoplastic” particles having a volume average particle size d2 _v50 such that d _{v 50} , more preferably d 2 _{v 50} ≧ 2.5 _× d _v50 , even more preferably d2 _v50 ≧ 5 _× d _v50 . Even more advantageously, the particles have a specific gravity 1.5 times, preferably 2 times, more preferably 4 times greater than the specific gravity of the original particles to be treated. It is also preferred that the "non-thermoplastic" particles have excellent heat transfer properties, thus permitting uniform temperature equilibrium in the mixing device, so that ferrite particles, magnetite and iron particles are preferred for use in the present invention. "Thermoplastic" particles.

Particles to be rolled and "non-thermoplastic"
The particles are present in the process of the invention in an amount of 100 parts by weight of “non-
It is mixed in a ratio of 3 to 15 parts by weight of particles to be rounded to "thermoplastic" particles.

The method of the present invention for rounding dry polymer particles, especially dry toner particles, can also be used while simultaneously rounding the particles and applying a coating thereto. In that case, a polymer material having a different composition than the resin already present in the polymer particles is added to the polymer particles, and preferably mixed therewith before adding the "non-thermoplastic" particles used for rolling. The polymer material used to apply the coating on the polymer particles can be in the form of a latex as well as in the form of polymer beads. In each case according to the invention, the polymeric material for the coating preferably has an average particle size smaller than the average particle size of the polymer particles to be coated, especially the dry toner particles. Suitably, the average particle size of the polymeric material used for the coating is at least 4 times smaller than the average particle size of the particles to be coated, preferably it is at least 10 times smaller. The polymeric material used for coating the particles can be an addition polymer having acrylate and / or methacrylate units, styrene units, and the like. It can also be a polycondensation polymer such as polyester, polyamide and the like. Using the method of the present invention, the inorganic particles or a mixture thereof can be embedded in the surface of the thermoplastic particles, and a mixture of the inorganic particles and the polymer coating material can be applied to the thermoplastic particles in the method of the present invention. .

The preferred concentration of particles to be coated on the "non-thermoplastic" particles is the highest surface coverage of the "non-thermoplastic" particles which can be calculated and / or visually observed by microscopy. At most 200%, preferably at most 100%, even more preferably at most 50%.

The process according to the invention, both for rounding only and for rounding and coating simultaneously, can be carried out in a mechanical mixing device, either a so-called rotorless mixer or a mixer with a rotor. This is probably due to some asperities or profiles (pro
Rotorless mixers, such as containers, which contain a plurality of non-filaments, thus allowing mechanical flow, are useful in the present invention, as well as containers that can be shaken, tumbled or rotated to induce mechanical movement. Means that. However, it is preferred to use a mixer that includes a rotor, for example, a mixer that is commercially available from Henschel, Lodige, and the like. Mixing should not reduce the quality of the particles but should allow for good flow. Preference is given to HENSSCHELL mixers, such as FM, which are equipped with a cooling device integrated in the wall and thus allow for excellent temperature regulation
4, FM10 type (product name) and the like.

The mixer can be filled with the ingredients, in which case at least 10% by volume and up to 90% should be filled. If it is less than 10%, no impact flow is recognized, and if it is more than 90%, good flow is not recognized. Preferably the mixer is filled from 35% to 75% of its volume.

Cooling can be easily performed. The mixture is cooled under static or dynamic conditions, for example by simply cooling the rounded mixer, or poured into a cold container and / or container.

After the rounding step, the treated particles must be separated from the "non-thermoplastic" particles. This can be an expensive fractionator from classical sieves, cyclones, fluidized bed separators, for example static NPK-static classifiers.
air classifiers and dynamic air classifiers
This can be done by any separation device known in the art, such as Care is taken to reduce the excessive mechanical impact on the non-thermoplastic beads so that they can be reused later, which makes the process more cost effective. If the treated particles are magnetic toner particles treated with non-magnetic "non-thermoplastic" particles, the particles can be separated by magnetic force. When non-magnetic toner particles are treated with magnetic "non-thermoplastic" particles, such as iron or ferrite particles, the same separation techniques can be used.

[0027]

EXAMPLE Preparation of Toner 1 (T1) 49 parts of a polyester of fumaric acid and di-propoxylated bisphenol A (ATLAC T500 is Atlas
Chemical Industries Inc. W
Ilmington, Del. U. S. A. Terephthalic acid (40 mol%), isophthalic acid (60 mol%) and di-
49 parts of polyester derived from a mixture of ethoxylated bisphenol-A (40 mol%) and ethylene glycol (60 mol%) together with 2 parts of Cu-phthalocyanine pigment (color index PB 15: 3) for laboratory use The mixture was melt-blended at 110 ° C. for 30 minutes in a kneader.

After cooling, the solidified mass is pulverized and
NE Fliessbettgegenstrahlm
Uhle 100AFG model (trade name), and milled using an ALPINE multiplex zig-zag classifier.
The fractionation was further performed using a 100MZR type (trade name). The average particle size of the separated toner
r Counter model Multisize
It was measured using r (trade name) and found to be 8.3 μm by volume. Specific gravity is 1.25 g / cm
³ (1250 Kg / m ³ ).

T _{p last} was determined by subjecting the toner to a load of 40 kg / cm ² at various temperatures for 10 minutes.
The temperature at which 10% permanent deformation was observed was taken as T _plast , which was 53 ° C.

Preparation of Toner 2 (T2) 34 parts of a polyester of fumaric acid and di-propoxylated bisphenol A (ATLAC T500 is Atlas
Chemical Industries Inc. W
Ilmington, Del. U. S. A. Terephthalic acid (40 mol%), isophthalic acid (60 mol%) and di-
34 parts of a polyester derived from a mixture of ethoxylated bisphenol-A (40 mol%) and ethylene glycol (60 mol%) are mixed with 2 parts of a Cu-phthalocyanine pigment (color index PB 15: 3) and 30 parts of hydrophobic SiO ₂ particles (AEROSIL R 97
2) Degussa AG, trade name of Germany)
And melt-blended at 110 ° C. for 30 minutes in a laboratory kneader.

After cooling, the solidified mass is pulverized and
NE Fliessbettgegenstrahlm
Uhle 100AFG (trade name), triturated with ALPINE multiplex jig-sag sorter
It was further separated using a 100MZR type (trade name). The average particle size of the separated toner is determined by Coulter Counter.
ter model Multisizer (product name)
And was found to be 12 μm by volume. Specific gravity is 1.45 g / cm ³ (1450 Kg /
m ³ ).

T _{p last} was determined by subjecting the toner to a load of 40 kg / cm ² at various temperatures for 10 minutes.
The temperature at which 10% permanent deformation was observed was taken as T _plast , which was 57 ° C.

Preparation of Toner 3 (T3) 98 parts of a polyester having a terephthalic acid and isophthalic acid part and a Tg 63 into which a mixture of di-ethoxylated bisphenol-A and ethylene glycol have been introduced are mixed with two parts of a Cu-phthalocyanine pigment (color The mixture was melt-blended with an index PB 15: 3) in a laboratory kneader at 110 ° C. for 30 minutes.

After cooling, the solidified mass is pulverized and
NE Fliessbettgegenstrahlm
Uhle 100AFG (trade name), triturated with ALPINE multiplex jig-sag sorter
It was further separated using a 100MZR type (trade name). The average particle size of the separated toner is determined by Coulter Counter.
ter model Multisizer (product name)
Was measured and found to be 8.2 μm by volume. Specific gravity is 1.2 g / cm ³ (1,200 kg
/ M ³ ).

Since this is a single resin toner, the Tg of the resin
Was adopted as T _plast , which was 63 ° C. Rounding Example Rounding Example 1 (RE1) 10 parts by weight of toner particles T1 were mixed with 100 parts of silica gel particles as "non-thermoplastic" particles. The silica gel particles have an average particle size of 49 μm and 2,200 Kg / m ³
Specific gravity. This mixture was charged to a HENSCELL mixer FM4 (trade name) with a 4 liter mixing chamber, resulting in a filling degree of 60% by volume. Mixer 500
It was operated at rpm (rotations per minute). Within 5 minutes, the mixer was brought to 50 ° C. and held at that temperature for a further 15 minutes.
Three samples of the mixture were taken at 5 minutes, 1 at 10 minutes and 1 at 15 minutes after mixing.

After cooling, the toner particles and the "non-thermoplastic" particles present in the four samples were separated on a wind separator. The treated toner particles separated from the three samples were observed under a scanning electron microscope (SEM). The shape was observed to be rounded. The degree of rounding is compared to the initial morphology of the particles on a scale ranging from D (initial particle morphology) through C and B to A (almost perfect rounding), and FIG.
And the shape of toner particles having quality A. The results are summarized in Table 1. A value of C + for rounding means that rounding is better than C, but not as good as B, and the same applies to B + with the necessary changes.

Rounding Example 2 (RE2) Silica gel particles were treated with an average particle size of 50 μm and 5000K.
Rounding Example 1 was repeated except that ferrite particles having a specific gravity of g / m ³ were changed. 5 parts by weight of toner particles
It was mixed with 00 parts by weight of ferrite particles. The results are summarized in Table 1.

Rounding Example 3 (RE3) Rounding Example 1 was repeated except that iron particles having an average particle size of 45 μm and a specific gravity of 7500 Kg / m ³ were used.
4 parts by weight of toner particles were mixed with 100 parts by weight of iron particles. The results are summarized in Table 1.

Rounding Example 4 (RE4) T _plast adopted from the Tg of the toner resin of 63 ° C.
Example 3 was repeated using toner particles T3 having the following formula: The results are summarized in Table 1.

Rounding Example 5 (RE5) Rounding Example 4 was repeated except at a mixing temperature of 62 ° C. The results are summarized in Table 1.

Rounding Example 6 (RE6) Rounding Example 3 was repeated except that toner T2 was used.
Rounding was performed at 65C. The results are summarized in Table 1.

Rounding Example 7 (RE7) Rounding Example 3 was repeated except that iron particles having an average particle size of 21 μm and a specific gravity of 7500 Kg / m ³ were used.
6.75 parts by weight of toner particles were mixed with 100 parts by weight of iron particles. The results are summarized in Table 1.

Rounding Example 8 Rounding Example 2 was repeated except at 10 times larger scale and at 60 ° C. The results are summarized in Table 1.

[0044]

[Table 1] d2 _v50 / d _v50: Non - Thermoplastic mean volume diameter to toner particles having an average ratio of the volume diameter of sg _nt / sg _t of particles: non - Thermoplastic ratio Example of the specific gravity of to toner particles having a particle 9: rounding and Coating 5 parts by weight of toner particles T1 and 0.15 parts by weight of dried and ground polymethyl methacrylate latex having a diameter of 0.15 μm were mixed together. The mixture is then treated with an average particle size of 45 μm and 5000 kg / m ^3.
Was added to 100 parts by weight of ferrite particles having the following specific gravity. This mixture is mixed with H having a mixing chamber volume of 4 liters.
The ENSCHELL mixer (FM4, trade name) was charged and resulted in a filling of 60% by volume. Mixer 500r
It was run at pm (rotations per minute). Within 5 minutes, the mixer was brought to 50 ° C. and held at that temperature for a further 15 minutes. 1
After 5 minutes, the resulting toner particles are rounded (rounding quality B)
And a clear, hard shell of methyl methacrylate polymer on the surface.

Example 10: Rounding and coating Using the same toner composition, but having an average particle size of 0.4 μm instead of polymethyl methacrylate latex,
Example 9 was repeated using 0.6 parts by weight of polymeric microbeads of co-poly (methyl methacrylate / dimethylaminoethyl acrylate) (Tg = 110 ° C.). Even after 5 minutes of rounding, moderate roundness (level C +) and good embedding of fine particles on the toner surface and filming were observed. The main features and aspects of the present invention are as follows.

1. -Average volume diameter d_v50And T_plastWith
Mixing the thermoplastic particles with the "non-thermoplastic" particles,
Is d2_v50≧ 1.5xd_v50Volume average particle size such that
d2 _v50And less than the specific gravity of the particles to be rounded
Also has a specific gravity 1.5 times greater;_plast-15 ℃ ≦ T
_mix<T_plastTemperature T such that it is + 30 ° C._mixAt
Mechanically mixing and rolling the thermoplastic particles; cooling the mixture; and recovering the rolled thermoplastic particles from the mixture.
Method for rolling thermoplastic particles containing floors.

2. - thermoplastic particles having a mean volume diameter d _v50 and T _plast polymeric coating material and - mixed with "non-thermoplastic" particles, the latter d2 _v50 ≧ 1.
5Xd _v has a volume average particle size d2 _v50 and at least 1.5 times larger specific gravity than the specific gravity of the thermoplastic particles such that _50, - the mixture at least 5 minutes, T _plast -15 ℃ ≦ T
mechanical mixing at a temperature T _mix such that _mix <T _plast + 30 ° C., coating the thermoplastic particles, cooling the mixture, and recovering the thermoplastic particles from the mixture. A method for coating plastic particles.

3. The method of claim 2 wherein the polymeric coating material is mixed with the thermoplastic particles to form a pre-mix prior to the addition of the “non-thermoplastic” particles.

4. The polymeric coating material is d
2 above having an average particle size at least 4 times smaller than _v50
Or the method according to item 3.

5. T _mix to T _plast -10 ℃ ≦ T _mix <T
A method according to any of the _{preceding claims} , wherein the method is chosen to be _plast + 30 ° C.

6. T _mix is T _plast ≦ T _mix <T _plast +3
A method according to any of the preceding claims, wherein the method is chosen to be 0C.

7. A method according to any of the preceding claims, wherein said "non-thermoplastic" particles are selected from the group consisting of crosslinked resin particles, highly filled resin particles and inorganic particles.

8. The method of claim 7 wherein said "non-thermoplastic" particles are selected from the group consisting of ferrite particles, magnetite particles and iron particles.

9. The “non-thermoplastic” particles have d2 _v50 ≧
A method according to any of the _{preceding claims} having an average volume diameter _d2v50 such that it is _2.5xdv50 .

10. 10. The method of any of the preceding claims, wherein the "non-thermoplastic" particles have a specific gravity at least four times greater than the specific gravity of the thermoplastic particles.

[Brief description of the drawings]

FIG. 1 shows scanning electron microscope images of a toner having a rounding quality D and a toner having a rounding quality A.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 101/16 C08L 101/00 // B29K 101: 12 (72) Inventor Daniel Heitzmann Belgium B 2640 malt cell・ Septes Trat 27 ・ Aghua-Gevert Na Murose Fennojasjap (72) Inventor Gerritt Derene Belgium 2640 Maltcell Septestrat 27 Inventor Geert Tersago Belgian Bee 2640 Malt Cell Septes Trat 27 Agfa-Gevaert Na Mrose Fennoutjap

Claims (2)

[Claims] 1. mixing thermoplastic particles having an average volume diameter d _v50 and T _plast with “non-thermoplastic” particles, the latter having a volume average particle size d such that d2 _v50 ≧ 1.5 _× d _v50
2 _v50 and at least 1.5 times greater than the particles of the specific gravity to be rounded and have a larger specific gravity, - the mixture at least 5 minutes, T _plast -15 ℃ ≦ T
mechanically mixing at a temperature T _mix such that _mix <T _plast + 30 ° C., rounding the thermoplastic particles, cooling the mixture, and recovering the rounded thermoplastic particles from the mixture. Method for rolling thermoplastic particles comprising. 2. _Mixing thermoplastic particles having an average volume diameter d _v50 and T _plast with a polymeric coating material and “non-thermoplastic” particles, the latter being d2 _v50 ≧ 1.5 ×
The volume average particle size such that d _v50 d2 _v50 and has at least 1.5 times larger specific gravity than the specific gravity of the thermoplastic particles, - the mixture at least 5 minutes, T _plast -15 ℃ ≦ T
mechanical mixing at a temperature T _mix such that _mix <T _plast + 30 ° C., coating the thermoplastic particles, cooling the mixture, and recovering the thermoplastic particles from the mixture. A method for coating plastic particles.