SE456119B - Toner particles for electrophotographic copying - Google Patents

Abstract

Toner for electrophotographic copying or electrostatic printing has (1) internally pigmented thermoplastic main particles prepd. by suspension polymerisation, mean dia. 2-25 microns, whose surface is covered by (2) a fine-grained thermoplastic polymerisable prepd. by emulsion or microssupension polymerisation, mean dia. 0.05-33% pref. 0.2-15% of mean dia. of main particles. 10-91% esp. 30-80%, of the surface of the main particles is covered by polymerizate. Methods of toner prepn. are also claimed.

Description

456119 10. 15. 20. 25. 2 gets copies. The adhesion of the particles to the photo-drum can be so strong that they do not fade either. This thereby bleaches from the "photo-drum of the cleaning systems which are transferred to be obtained intended to remove * toner residues, which are not paper. Due to this strong adhesion soon a strong deterioration of the quality of copies obtained.

We have now found that if pigmented toner particles are first (with the pigment produced by the suspension polymerization monomer) and then coated than particles already mixed in with polymer particles which are substantially less self-contained at all, "lumpy" spherical having the adhesion may even become the toner particle which does not the disadvantage of strong adhesion to toner produced by the conventional milling method. for electrostatic printing the photo drum. lower than for the invention thus refers to a toner electrophotographic copying or to a method of producing one with the features specified in the claims. on the toner pair Application of the small polymer particles on such a surface that UIOHOIHEFEF can be carried out technically whole from until the toner particles become economically advantageous. The way the particles are coated The process The base particles are produced by suspension polymerization. First, monomers, monomer-soluble initiator, pigments and possibly the charge regulator and dispersion using a suitable colloid system. ring pigment. The mixture is emulsified in water. After evacuation, the temperature for polymerization is raised to 2-25, whereby risk particles are obtained. The average diameter of these may be 30 .mu.m, preferably 3-15 .mu.m. 35.

By internally pigmented base particle is meant particles which are prepared in such a way that the pigment is mixed with the monomer before polymerization and thereby is more or less evenly distributed in the finished polymerized base particle. For the position of the base particles, styrene and various As monomers, alone or in admixture, derivatives of styrene, esters of acrylic acid or methacrylic acid, acrylonitrile, vinyl chloride, vinyl fluoride, vinylidene fluoride, 10. 15. 20. 25. 30. 35. 456119 Vinyl acetate, etc. To achieve some crosslinking, multifunctional monomers can be used, for example divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, etc. The amount of crosslinker can be up to 10 Z, preferably up to 1 X of the monomer mixture.

In the preparation of the base particles, mono-, for example, dialkyl peroxydicarbonate soluble initiators, esters, tert-butyl peroxy pivalate, octanoyl peroxide, lauroyl peroxide, tert-butyl peroxy-2-ethylhexanoate, benzoyl peroxide, 2,2'-azobisisobutyl -valero-nitrile and similar compounds.

As a protective colloid, the colloid system for the production of colloids in the base particles can be used water-soluble of the cellulose derivative type, silicic acid type, etc. polyvinyl alcohol, etc. or powder stabilizers of sparingly soluble phosphates, metal hydroxides. The powder stabilizers are preferably used together with a suitable co-stabilizer. organic cases that As a dye in the base particles, black was used to pre-surface the pigments for dyes magnetite or Carbon etc. some it is advisable that they should remain finely divided inside the Size 1 monomer droplets. on the fine-grained particles form bulges surface should be than Thus, on the fine-grained particles should be a maximum of about 33 Z preferred- Size- SOIH on the substantially smaller base particle itself. the diameter shows a maximum of 15 X of the diameter of the base particle. the boundary down is determined the smallest size that the desired to Already "knobs" in the order of 0.005 μm give reduced they have grain size in the range 0.005-5; n, preferably 0.02-2 / J fl l- of gives the effect of reduced adhesion phototrum. adhesion. Suitably, the fine-grained particles may have a one-factor surface area other than the degree of coverage, i.e. the proportion of the base particle that is covered by Tåtast 91 Z of the fine-grained particles of the base particle. coverage corresponds to area. However, it is not necessary to use the degree of coverage possible to reduce the degree of adhesion to the degree of coverage of the photo drum to such a high degree of coverage. _50 Z Has been shown to give 456119 10. 15. 20. 25. 35. 4 very strong reduction in adhesion. However, a positive effect is obtained already at 20 Z coverage. The coverage should thus be between 20 Z and 91 Z, preferably 30- 80 Z.

In principle, one strives to have only the fine-grained particles in a monoparticulate layer, but at least in part the layer can be several particles thick.

It is desirable that the fine-grained particles are firmly anchored in the surface of the base particles. This can be achieved by softening the base particles by small amounts of plasticizer or by heating. As a result, the fine-grained particles can be melted into the surface. It is convenient for the fine-grained particles to melt into the base particle to a depth corresponding to about half the diameter of the fine-grained particle.

The small polymer particles that are laid on the surface of the base particles must be mainly spherical and can be prepared by emulsion polymerization or microsuspension polymerization.

In the preparation of the fine-grained particles according to emulsion polymerization, monomers are emulsified in water with the aid of emulsifiers. For initiation, water-soluble initiator of the type persulphate, hydrogen peroxide, hydroperoxide, etc. is selected.

After polymerization, a latex of very fine-grained polymer particles is obtained.

In the preparation of fine-grained V particles according to the microsuspension polymerization method, monomer-soluble initiators of a similar type as indicated for the base particles are preferably used. In the microsuspension method, the charge can be mixed with The monomers can also be regulated. mix in dyes. The monomer mixture is then emulsified in water using emulsifiers and high shear forces ”.

The polymer composition in the fine-grained particles on the surface of the base particles may be the same as in the base particle. However, it may be advantageous to choose a more high melting polymer type in the fine grain particles on the surface. Namely, a higher melting point entails less risk of them agglomerating among themselves in the fine-grained particles u 10. 15. 20. 25. 30. 35. 456119 instead of being adhered to during the application operation. In order to make the fine-grained particles particularly difficult to melt, the surface of the base particle on the surface can be melted to a greater degree than the base particles.

The fine-grained particles can be laid on the surface of the base particles according to both wet and dry methods.

According to a particular embodiment of the invention, the toner is prepared in such a way that an aqueous dispersion of the pigmented base particle is brought into contact with a latex of the fine-grained polymer, after which a protective colloid system is formed in the aqueous dispersion and the temperature is raised so that the fine-grained particles adhere to the base particle. when suitably prepared according to this method, the protective colloid system used for the suspension polymerization step of the base particles is first deactivated. If, for example, certain inorganic powder stabilizers have been used as protective colloids, these can be dissolved by acidifying the aqueous suspension of base particles. Then slowly add the latex of the fine-grained particles. In this case, one should have such conditions that the latex of fine-grained particles does not fall immediately when it enters the suspension, risking instead of base particles. Namely, there is then a de for depositing on the surface of the base particles. the small grains in the latex agglomerate with each other After stirring for a certain time, the fine-grained particles have precipitated on the surface of the base particles. Then the system for regeneration of the protective colloid system is alkalized. There is thus no risk of agglomeration of the particles as the dispersion is heated to fuse the fine-grained particles into the surface of the base particles. It is then acidified and washed. i To give the correct triboelectric charge to the toner, the fine-grained particles on the surface must have a fixed tribo charge.

Such triboelectric properties can be achieved by subsequently precipitating a charge regulating substance on the surface of the coated particles. If the small surface particles are prepared by microsuspension polymerization, 45 456 10. 15. 20. 25. 30. 35. 119 regulating agent may alternatively be mixed into the monomer before the Finally, the chemical composition of the small surface pairs may need to be added such already polymerization of fine-grained the particles. not on gives positive triboelectric charge are fine-grained particles the particles are selected as one by extra charge regulator. Examples are particles such as polyacrylonitrile or amino-containing monomer. When using fine-grained particles of polyvinyl chloride, fluoropolymer, etc., negative triboelectric charge is obtained. the basic particles When applying the fine-grained particles according to the method, dry and then invest in one to keep the advantageous YIOFF mixer. For the powder bed in an even mixture, larger balls, such as 5 mm glass balls, can also be mixed in. The small polymer grains that are to be laid on the surface are then loaded onto the powder bed. The small grains can either be present as a dispersion in a suitable liquid, the liquid being evaporated in the powder bed, or in the form of a very fine-grained already dried powder. The powder bed temperature is raised during continued mixing. The fine-grained particles then adhere to the surface of the base particles and melt at the higher temperatures partially into the base particle.

An alternative way to melt the small polymeric SOIII surface on the base particles is to coat the mixed short zone heated to 150-400 ° C depending on the residence time the particles in the base particles into an air stream below one in the hot zone.

The invention is further elucidated in the following exemplary embodiments. In the examples, parts and percentages refer to parts by weight and percentages by weight, respectively, unless otherwise stated.

Preparation of fine-grained polymer 1.89 was charged in Example 1: 40 g total styrene, sodium dodecyl sulfate and water 395 g 500 ml equipped stirrer and valve for evacuation and nitrogen to 80 ° C. at the same time as for glass flask with cooler, additive. heated At 80 ° C the 3.5 Z mixture was placed under a nitrogen atmosphere. ef! The mixture was stirred with stirring. 5 g of hydrogen peroxide. The polymerization was then allowed to proceed for 12 hours, 10 .mu.g of seed latex.

ZOO g which resulted in a 0.11 / Mm 120 g of the above seed latex, 5 g / kg of sodium S. 10. 15. 20. 25. 30. 35. 456119 7 sodium dodecyl sulfate, 0.4 g of about SO 2 divinylbenzene , 27.6 g of styrene and water to a total of 395 g, were charged in the same equipment as above and then followed the same procedure.

This was obtained with a particle size of 0.16 .mu.m. a crosslinked 10 Z polystyrene latex Example 2: Preparation of fine-grained polymer 250 g of styrene, 0.8 g of neozapone schuarts X 51 charge (from BASF) and 2.5 g of 2,2'-azobis (2,4-dimethyl) was invested in as in valeronitrile regulators) the same equipment example 1. heated mass polymerization was allowed to proceed at 8S ° C, which resulted in viscosity increase at 24 ° C from 10.5 to 13 seconds (Ford cup, nozzle 4 mm).

The monomer mixture and for 2 hours a 198 g mass polymer, 2 g about 50 Z divinylbenzene, 7 g 2,2'-azobis (2,4-dimethylvaleronitrile) were emulsified together with 828 g 3 g / kg sodium dodecyl sulphate in an Ultra Turrax under some minute.

The emulsion was then charged to a two-stage Manton Gaulin homogenizer, after which 1 g of sodium dodecyl sulfate was charged to a 1.5 L glass autoclave which was placed under a nitrogen atmosphere. at 65 ° C 12 0.19 μm polystyrene microsuspene The emulsion was polymerized for hours. In this way a 19 Z sion with polymerized charge controller was obtained.

Example gel 3: Preparation of base particle To was added solution and to It a solution of 2 kg 0.16 molal trisodium phosphate with stirring S20 g 1.0 molal calcium chloride end 150 g 0.2% sodium dodecylbenzenesul- obtained was diluted to 2965 g with 0.2 Z potassium dichromate solution and constitutes dispersion phonate solution. now the mixture ring medium. 700 g of styrene, 300 g of butyl methacrylate, 80 g of soot "Printex V" X S1 (BASF) in a bead mill to a dispersed carbon monomer dispersion. 10 g were dissolved in 990 g with the dispersing medium (Degussa) and 3 g of neozapon schwartz were triturated with 2,2'-azobis (2,4-dimethylvaleronitrile) together with mixed carbon monomer dispersion and charged (2965 g) to the mixture was added under a nitrogen atmosphere and was allowed to polymerize from an autoclave. under rapid and further at 85 ° C for 1 hour room temperature heating and moderate stirring. The mixture was cooled to room temperature, and the pH was adjusted to about 3 with 35 g of 2,2'-azobis (2,4-dimethylvaleronitrile) charged.

After stirring for a few minutes, the pH was adjusted to about 9, the mixture being recycled through a "Ystral" dispersing unit (Bergius Trading AB) and emulsified to a suitable droplet size for toner particles. The autoclave was again placed under a nitrogen atmosphere and allowed to polymerize for 18 hours at 6S ° C and moderate stirring. The suspension was then cooled to room temperature.

An aliquot of the polymer was transferred to a vessel and the pH was adjusted with HCl to 2, dissolving calcium phosphate, which acts as a protective colloid. The suspension was filtered and washed first with acidified water and then with pure water to finally dry at 35 ° C.

In this way, toner particles were obtained with a grain size of about 10 μm and with a charge of -12 pC / g towards Höganäs carrier. Copying attempts with the toner in the Mita DC 313 Z initially gave a good copying result, but soon the reproducibility deteriorated due to strong adhesion of the spherical, smooth toner particles to the photo drum.

Example 4: Coating of the base particles with fine-grained particles 362 g of 10 Z polystyrene latex prepared according to Example 3, 390 g of 1.5 g / kg of sodium dodecyl sulphate and 2 l of water were mixed to form the coating dispersion. 2 kg of 1.5 g / kg of sodium dodecyl sulfate were charged to an autoclave containing a polymer prepared according to Example 3 and then the pH was adjusted to 2 with HCl. The coating dispersion was charged for 20 minutes with good stirring, and then mixed for a total of 1 hour before raising the temperature to 6S ° C. At 65 ° C, the pH was adjusted with NÉ3 to 8.3 and the temperature was further raised to 90 ° C.

After less than 5 minutes at 90 ° C, the now coated toner suspension was cooled to room temperature.

Then the pH was adjusted with HCl to 2, whereby calcium phosphate; which acts as a protective colloid, was dissolved. The suspension was filtered and washed first with acidified water and then with clean water. The sample was then doped with 10. 15. 20. 25. 30. 35. 456119 9 0.05 Z neozapan schuartz X 51 in water and mixed in 1 X-methanol solution by the charge regulator, then filtered again. This action is necessary because the PS particles on the surface of the base particle shield the effect by the filter cake after washing being slurried with one of the charge regulator in the base particle.

Examination with a scanning electron microscope showed that the polystyrene particles had been adsorbed by the base particle melt length and due to the temperature treatment into polystyrene particles was adjusted so that about 50 Z of the base EV base particles was about half its volume. The surfaces of the particles were covered by the projection of the latex particles. In this way a lumpy surface, which gave a charge of -14 @ pC / g towards Höganäs Mita DC 3132, from the beginning the reproducibility still gave a smooth surface. you got toner particles with a carrier. Copy attempt in good copies and was 30,000 copies. and very a particularly well coated well after One can note background clean copies. The photo drum was only with small amounts of toner that could be easily removed.

Example S: Coating of the base particles with fine-grained particles Base particles are prepared in the same manner as in Example 3 and coated according to Example 2. with 218 g of 19 Z-poly polystyrene latex prepared had to approximately Microscope examination showed that the particles melted half their volume and surface coverage was also here in adsorbed and into the basic particles in the order of magnitude S0 X. In this way, lumpy toner was obtained- there was a charge of -17 Cpt / g. charge regulators, which had similarity to the toner according to example 4 excellent copying properties, the knobs gave a This toner also in creates.

Example 6: The procedure of Example 4 was repeated, except that the amount of latex was reduced to 228 g.

The microscope examination showed a lower degree of coverage, approx. 30-35 Z in 4. comparison with what was obtained according to example toner particles with better produced, the copy particles were obtained. Despite this, the toner particles according to example 3.

Claims (9)

456119 10 15 20 25 30 35 10 Patent claim Knotty toner for electrophotographic copying or electrostatic printing, characterized in that it comprises an internally pigmented thermoplastic base particle made by suspension poly-. merisation with an average diameter in the range 2-25 μm, the surface of which is coated with a fine-grained polymer prepared by emulsion or microsuspension polymerization with a particle size with an average diameter of 0.05-33% of the average particle diameter, with 20-91% of base the surface of the particle is coated with the fine-grained polymer seat. 2. Toner according to claim 1, characterized in that the average diameter of the fine-grained polymer is 0.2-15% of the average diameter of the base particle. Toner according to Claim 1 or 2, characterized in that 30-80% of the surface of the base particle is coated with the fine-grained polymer. Toner according to one of the preceding claims, characterized in that the fine-grained polymer is also pigmented. 5. Toner according to claim 1, 2 or 4, characterized in that the melting point of the fine-grained particles is> 10 ° C higher than that of the base particles. Toner according to Claim 1, 2, 4 or 5, characterized in that the fine-grained particles are produced by microsuspension polymerization and contain a charge-regulating substance. A method of producing gnarled toner for electrophotographic copying or electrostatic printing according to claim 1, characterized in that an aqueous dispersion of an internally pigmented thermoplastic base particle prepared by suspension polymerization and having an average diameter in the range of 2-25 μm brought into contact with a latex of a fine-grained polymer having a particle size having an average diameter of 0.05-33% of the average diameter of the base particle, after which a protective colloid system is formed in the water dispersion and the temperature is raised so that the fine-grained particles adhere to the base particle. surface to a coverage of 20-91% of the surface of the base particle. 8. A method according to claim 7, characterized in that the aqueous dispersion of the pigmented base particle consists of polymerization serum from the polymerization of the base particle. 9. A method according to claim 8, characterized in that the protective colloid system is deactivated before the addition of the latex of the fine-grained polymer, and that the protective colloid system is regenerated. before the temperature