WO2003052522A1

WO2003052522A1 - A process to prepare an amorphous polyester and a toner composition

Info

Publication number: WO2003052522A1
Application number: PCT/NL2002/000811
Authority: WO
Inventors: Augustinus Eugene Henk Keijzer De; Matthias Jozef Gertruda Brouns; Jacob Leendert Haas De
Original assignee: Dsm N.V.
Priority date: 2001-12-17
Filing date: 2002-12-10
Publication date: 2003-06-26
Also published as: AU2002351447A1

Abstract

The invention relates to a toner composition containing an amorphous polyester. The polyester is obtained by a process comprising three steps: in the first step a reaction of a dicarboxylic acid or its derivative with a molar excess of diol takes place, in the second step the polycondensation of the prepolymer of the first step into a hydroxyfunctional polyester takes place and in the third step the hydroxyfunctional polyester resin is converted into an acid functional polyester by reaction of the hydroxyfunctional polyester with a dicarboxylic acid or its anhydride.

Description

A PROCESS TO PREPARE AN AMORPHOUS POLYESTER AND A TONER COMPOSITION

The present invention relates to a process to prepare an amorphous polyester and a toner composition comprising this polyester.

As disclosed in "Electrography and development physics" by L.B. Schein (Volume 14, pages 26-49, Springer Verlag, 1988), electrography is a complex process involving, in most embodiments, distinct steps being charging, exposing, developing, transfer, fusing and cleaning. During the development step the toner particles are brought into the vicinity of the latent electrostatic image. By virtue of the electric field the toner adheres to the latent image, transforming it into a real image. Next the developed toner is transferred to the paper. The image is fixed to the paper by melting or fusing the toner into the paper surface. The fusing of the toner onto or in the paper may be done by non-contact heating techniques, such as for example flash fusing, and by contact heating techniques such as for example press heating by means of heat rollers. The latter heating technique is mainly used since the most efficient heat transfer may be achieved allowing for high speed during the fixing step.

A toner composition may comprise a resin, a colorant, a charge control agent, magnetic material, carrier material and/or additives. The resin is responsible for important properties such as for example the pulverizability, the pigment dispersability, the blocking resistance, the electric properties, the fixing properties and the offset resistance. Suitable resins to be used in toner compositions may be for example epoxy resins, polyester resins, polystyrene resins, (meth)acrylate resins and styrene (meth) acrylates.

The use of heated rollers in the fixing step requires the use of a resin that may be fixed at a low temperature and prevents offset to the heated rollers. A polyester may be used because of the excellent low temperature fixing properties. Branched and crosslinked resins have been proposed already to prevent the occurrence of hot offset of the toner to the heated fuser rolls. These branched and crosslinked polyesters may be obtained by a process as disclosed in for example US- A-3,938,992, DE-A-3,518,414 or EP-A-312691. It is the object of the present invention to provide a resin to be applied in a toner composition resulting in the desired good low-temperature fixability and in the required offset resistance whereas the resins and the toners do not show the drawbacks as mentioned above.

The toner composition according to the invention comprises an amorphous polyester obtained by a process comprising three steps: in the first step a reaction of a dicarboxylic acid or its derivative with a molar excess of diol takes place, in the second step the polycondensation of the prepolymer of the first step into a hydroxyfunctional polyester takes place and in the third step the hydroxyfunctional polyester resin is converted into an acid functional polyester by reaction of the hydroxyfunctional polyester with a dicarboxylic acid or its anhydride.

The amorphous polyester is a substantially non-crosslinked polyester. The amorphous polyester is highly branched. In the third step, the hydroxyl functional polyester obtained in the second step having all desired properties for use in the toner composition, except for acid value, is converted into an acid functional polyester without negative influence on the desired toner properties already obtained in the second step. It is an essential advantage of the present invention that the hydroxyl functional polyester is converted into an acid functional polyester without decrease of the viscosity properties.

The polyester resin for dry toner has excellent offset resistance The toner composition according to the present invention shows simultaneously a low-temperature fixability, anti-blocking properties and a high temperature offset resistance.

The dry toner may be used for developing an electrostatic image in electrophotography, electrographic recording or electrostatic printing. Generally, a polyester may be prepared by esterification or transesterification, whether or not in the presence of customary catalysts such as for example dibutyl tin oxide or tetrabutyltitanate. The polyester resin is produced by a condensation reaction of a dicarboxylic acid or its lower alkyl ester with a diol by direct esterification or by ester interchange. The preparation may be conducted in both a batch process as well as in a continuous process. General knowledge of polyesters is described in for example Encyclopedia of Polymer Science and Technology, Vol. 12, pages 1-75, Wiley-lnterscience, New York, 1988 (ISBN 0-471-80994-6).

According to the present invention the polyester is obtained by the esterification of a dicarboxylic acid or the transesterification of a derivative of the dicarboxylic acid, in the presence of a molar excess of a difunctional alcohol in the first step. The derivative may be for example the (C C ) alkyl ester, the anhydride or the acid chloride of the dicarboxylic acid.

The amount of molar excess of diol may be selected depending on the specific application. Preferably, the molar ratio dicarboxylic acid or the derivative of the dicarboxylic acid : diol is between 1 :1 ,1 and 1 : 4,0 and more preferably this ratio is between 1 : 1 ,2 and 1 : 2,0.

Suitable dicarboxylic acid to be applied in the first step includes for example phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, terephthalic acid, pyromellitic acid, trimellitic acid, 3,6-dichlorophthalic acid and tetrachlorophthalic acid. The polyester may also be obtained from the derivatives such as for example the anhydrides, acid chlorides or the lower, for example C C , alkyl esters thereof. The carboxylic acid component generally consists of at least 50 mole %, preferably at least 70 mole %, of isophthalic acid and/or terephthalic acid.

Cycloaliphatic and/or acyclic polycarboxylic acids such as for example cyclohexane dicarboxylic acid (CHDA), tetrahydrophthalic acid, hexa hydro endomethylene terephthalic acid, hexahydrophtalic acid, hexachloro-tetrahydrophthalic acid, azelaic acid, sebacic acid, decane dicarboxylic acid, dimer fatty acid, adipic acid, succinic acid and maleic acid and their anhydrides may be used in amounts of up to 30 mole % and preferably of up to 20 mole % of the total of carboxylic acids. Hydroxycarboxylic acids and/or lactones, such as for example 12-hydroxystearic acid and epsilon-caprolactone may also be applied.

Suitable difunctional alcohols include for example ethylene glycol, 1 ,2-propanediol, 1 ,3-propanediol, 1 ,2-butanediol, 1 ,4-butanediol, 1 ,3-butanediol, 2,2- dimethyl-1 ,3-propanediol (= neopentyl glycol), the hydroxypivalic acid ester of neopentyl glycol, 2,5-hexanediol, 1 ,6-hexanediol, 2,2-[bis-(4-hydroxy-cyclohexyl]- propane, 1 ,4-dimethylol cyclohexane, diethylene glycol, dipropylene glycol, polyoxypropylene-(n)-polyoxyethylene-(n')-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (n)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene (n)-2,2-bis(4- hydroxyphenyl)propane, and polyoxypropylene (n)-hydroquinone (wherein each of n and n' is a number of from 2 to 6).

Minor amounts of multi-functional acid such as for example, trimellitic acid, trimellitic anhydride, pyromellitic acid, trimesic acid, anhydrous methyl trimellitate, anhydrous ethyl trimellitate, t methyl trimellitate and tetracarboxylic benzene may be used. Generally, the units of these acids are present in the polyester in an amount less than 25 % by weight relative to the total amount of monomers. Preferably this amount is less than 10% by weight.

Minor amounts of multi-functional alcohol units such as for example glycerol, hexanetriol, pentaerythritol, sorbitol, trimethylol ethane, ditrimethylol propane, trimethylol propane and tris-(2-hydroxyethyl)-isocyanurate may be added to the above mentioned di-functional monomers to form a highly branched structure to provide the desired offset resistance during the fixing step.

The multi-functional alcohol units may be present in an amount less than for example 25 % by weight relative to the total amount of monomers. Preferably this amount is less than 10% by weight.

The reaction in the first step results in a low molecular weight hydroxy functional prepolymer and the reaction is usually conducted in a stirred tankreactor, or in a cascade of reactors, at ambient pressure. The reaction may take place in the presence of an esterification or ester interchange catalyst such as for example sulfuric acid, titanium butoxide, dibutyltin oxide, magnesium acetate or manganese acetate

Next, the second step comprises the polycondensation of the prepolymer obtained in the first step into a high visco-elastic hydroxy functional polyester under a reduced pressure of at most 30 mmHg and preferably between 3 and 5 mmHg while distilling off the diol component. Preferably, the hydroxyl functional polyester has an hydroxyl value between 2 and 50 mg KOH/gram resin and more preferably this value is between 3 and 30 mg KOH/gram resin.

Preferably, the hydroxyl functional polyesters obtained in this second step has an acid value lower than 2 mg KOH/gram resin. The polycondensation is basically an equilibrium reaction, therefore it is neccessary to completely remove the reaction products, for example the diol, released during the polycondensation in order to obtain the desired molecular weight or degree of polymerisation. During the reaction in the second step a polymerization catalyst such as for example titanium butoxide, dibutyltin oxide, tin acetate, zinc acetate, tin disulfide, antimony trioxide or germanium dioxide may be present. During the reaction the visco elastic properties of the product are monitored by a torque meter connected to the stirrer.

In the third step, the hydroxyl functional polyester resin obtained in the second step is converted by the reaction with a dicarboxylic acid or its anhydride into an acid functional polyester having an acid value between for example 0.5 and 25 mg KOH/gram resin, and preferably between 2 and 20 mg KOH/gram resin.

Suitable dicarboxylic acids include for example phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, terephthalic acid, pyromellitic acid, trimellitic acid, 3,6-dichlorophthalic acid and tetrachlorophthalic acid.

Preferably, the dicarboxylic acid is terephthalic acid.

Preferably, the acid value of the polyester is within the range between 0.5 and 25 mg KOH/gram resin and more preferably this value is in the range between 2 and 20 mg KOH/gram resin. The acid value is of importance because acid values lower than 0,5 mg KOH/g tend to result in bad coloring agent dispersibility. Whereas on the other hand, if the acid value exceeds 25 mg KOH/gram resin, the humidity dependency of the chargeability tends to be substantial.

The glass transition temperature (Tg) of the polyester is preferably in the range of between 30°C to 90°C, and is more preferably in the range of between 55°C to 75°C.

Preferably, the polyester has a dynamic viscosity η (120°C, 1 rad/sec) between 1000 and 100000 Pas, a dynamic viscosity η (180°C, 1 rad/sec) between 1 and 3000 Pas and a phase angle δ (120°C,1 rad/sec) between 40 and 80 degrees.

The dynamic viscosity and the phase angle are determined according to ASTM D440-95A.

The toner composition according to the invention may comprise the polyester as the resin, a colorant, a charge control agent, magnetic material and/or additives. The selection and the amount of these components depend of the specific end-use. The polyester may also be mixed with at least one resin selected from for example a polyester, polyamide, polyolefine, styrene (meth)acrylate, styrene butadiene, crosslinked styrene polymer, epoxy resin, polyurethane, vinyl resin and/or polyester imide in an amount less than 50 % by weight ( relative to the polyester according to the present invention). This mixture may be applied as the resin component in the toner composition.

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

The charge control agent may be incorporated in the toner in an amount between 0.1 and 8.0% by weight, preferably between 0.2 and 5.0% by weight, based on the amount of the binder resin.

The dry toner may be used, for example, for developing an electrostatic image in electrography, electrostatic recording or electrostatic printing.

A toner may, for example, be obtained by uniformely dispersing additives such as for instance, a colorant, a charge control agent, a magnetic material and/or a modifier into the polymer. The resulting mixture is melt kneaded, cooled, pulverized, and then classified to thereby obtain a toner having an average particle diameter of 5 to 15 μm. This toner may be mixed with a carrier powder, for example, an iron oxide carrier, a spherical iron oxide carrier, or a ferrite carrier, to give a dry two- component developer. In this case, the carrier is used as it is or after being coated with a resin or another material. It is also possible to apply a chemical method to obtain the toner using the polyester according to the invention.

In the case of producing a one-component toner using the polyester resin according to the invention of the magnetic material used may be a powder of a ferromagnetic metal such as for example iron, cobalt nickel alloy or another alloy or compound containing an element exhibiting ferromagnetism such as for example ferrite, hematite or magnetite. The magnetic material may be used in the form of a fine powder having an average particle diameter of from 0.1 to 1 μm and the amount of the magnetic material dispersed into the binder resin may be from 30 to 70 parts by weight per 100 parts by weight of the binder resin. .

US-A-5548059 discloses unsaturated linear polymers having repeating units of a reaction product of a first monomer, a second monomer, a third monomer an optionally a fourth monomer. In contrast to the present invention, the monomers and the catalyst undergo transesterification to form the polymer. Furthermore, US-A-5548059 does not disclose the reaction of a hydroxyl functional polyester into an acid functional polyester.

US-A-5486444 discloses a crosslinked polyester obtained by reaction of a polyhydroxy functional polyester with a dianhydride or a diepoxy functional crosslinking component. This crosslinking reaction does not result in an acid functional polyester. Furthermore the viscosity will change because of the crosslinking whereas in the present process the viscosity value does not change because of the specific reaction in the third step.

The invention will be elucidated by means of the following non- restrictive examples

Example I

Preparation of a polyester resin

Isophtalic acid (0.65 mol), terephtalic acid (0.98 mol), trimethylolpropane (0.05 mol) and ethylene glycol (3.25 mol) were introduced into a heated reactor equipped with an anchor stirrer, a stirrer torque meter and an appropriate distillation column. To the reactor 0.5 mmol methylbutyltinoxide was added as a catalyst. The first step, the esterification reaction, was conducted under atmospheric pressure while maintaining the internal reaction mixture temperature at a level of 185°C to 220°C. After about 4 hours after the distillation of water started, the reaction mixture became transparent and the distillation of water stopped. The torque meter of the stirrer showed a value of 20 Ncm at 200 rpm.

In the second step, the polycondensation reaction, while maintaining the internal temperature at 220°C -240°C and the stirrer rotational speed at 200 rpm, the pressure of the reactor was gradually reduced to 7-8 mbar, allowing the excess of ethylene glycol to distill off from the reactor and causing the stirring torque to gradually increase. After 1 ,5 hours the stirring torque reached its final value of 30 Ncm, at which point the pressure was slowly changed to atmospheric.

In the third step, the acidification of the resin, 132.5 mmol of terephtalic acid was introduced in the reactor, causing the stirrer torque to drop to 15 Ncm at 200 rpm. The mixture was allowed to homogenize at atmospheric pressure, after which the pressure was again slowly reduced to 7-8 mbar to induce the coupling reaction. After the stirrer torque had reached the desired level of 30 Ncm, the pressure was adjusted to atmospheric pressure, thus terminating the reaction. The stirring was continued for another hour to make sure the resin was stable.

The characteristics of the obtained resin were as follows: a Tg (midpoint, 2^nd heating curve) of 71 °C, a dynamic viscosity (DMS, 120°C, 1 rad/s) of 51000 Pa.s, - a phase angle δ (DMS, 120°C, 1 rad/s) of 52° , - an acid value of 20 mg KOH/g and Shimadzu flow tester (2.0 g, capillary 1-1 mm, 6 min heating rate, 20 kg load) temperatures T1-T4 of 140°C -161 °C.

Comparative Example A Preparation of a polyester resin

Example I was repeated except for the acidification after the second step.

The characteristics of the obtained resin were as follows a Tg (midpoint, 2^nd heating curve) of 65°C, - a dynamic viscosity (DMS, 120°C, 1 rad/s) of 50000 Pa.s, - a phase angle δ (DMS, 120°C, 1 rad/s) of 51 °, an acid value < 2 mg KOH/g and

Shimadzu flow tester (2.0 g, capillary 1-1 mm, 6°/min heating rate, 20 kg load) temperatures T1-T4 of 142°C -163°C.

Example II

Preparation of a toner composition

A toner was prepared by adding to an extruder 5600 grams of polyester resin obtained according to Example I, 173 grams pigment (Cyan pigment Heligon Blue of BASF) and 106 grams charge control additive (Bontron E-84 of Orient).

The resulting extrudate was crushed and milled to an average particle size (mean) of 7 micrometer.

The Tg as measured with Differential Scanning Calorimetry (DSC), using a heating rate of 10 degrees per minute and determining the onset of Tg from the second heating curve, was 67 °C.

The viscosity of the toner at 120 °C and 1 rad/second measured with dynamical mechanical spectroscopy was 48500 Pa.s.

The charge to mass ratio of the toner was -52 microcoulomb per gram (as measured against a Ferrite carrier with an average particle size of 50 micrometer and coated with a siloxane resin using a Faraday cage charging device (q/m meter from Epping GmbH)).

Claims

1. A process for the preparation of an amorphous polyester comprising three steps: - in the first step a reaction of a dicarboxylic acid or its derivative with a molar excess of diol takes place, in the second step the polycondensation of the prepolymer of the first step into a hydroxyfunctional polyester takes place and in the third step the hydroxyfunctional polyester resin is converted into an acid functional polyester by reaction of the hydroxyfunctional polyester with a dicarboxylic acid or its anhydride

2. A process according to Claim 1 characterised in that in the first step the molar ratio dicarboxylic acid or the derivative of the dicarboxylic acid : diol is between 1 :1 ,1 and 1 :4,0.

3. A process according to any one of Claims 1-2 characterised in that the hydroxyl value of the hydroxy functional polyester in the second step is between 2 and 50 mg KOH/gram resin.

4. A process according to any one of Claims 1-3 characterised in that the acid value of the acid functional polyester in the third step is between 0,5 and 25 mg KOH/gram resin.

5. A process according to of Claim 4 characterised in that the acid value of the acid functional polyester in the third step is between 2 and 20 mg KOH/gram resin.

6. A process according to any one of Claims 1-5 characterised in that the dicarboxylic acid in the third step is terephtalic acid.

7. A toner composition containing an amorphous polyester obtained by a process according to any one of Claims 1-6.

8. A toner composition according to Claim 7 characterised is that the polyester is a substantially non-crosslinked polyester.