WO2009037459A1

WO2009037459A1 - Toner, process for preparing toner. use and method of imaging

Info

Publication number: WO2009037459A1
Application number: PCT/GB2008/003166
Authority: WO
Inventors: John Dylan Morgan; Zoonia Mehmood
Original assignee: Fujifilm Imaging Colorants Limited
Priority date: 2007-09-22
Filing date: 2008-09-19
Publication date: 2009-03-26
Also published as: GB2465705A; GB201003024D0; GB2465705B; GB0718551D0

Abstract

A toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A of average primary particle size not greater than 10nm; ii) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and iii) a surface additive C of average primary particle size greater than 30nm; wherein the surface additives A, B and C each comprise a silica.

Description

TONER, PROCESS FOR PREPARING TONER. USE AND METHOD OF

IMAGING

The invention relates to toner suitable for electrophotography, to processes for preparing the toner, to uses of the toner and imaging methods using said toner.

Electrophotography encompasses image forming technologies such as, for example, photocopying and laser printing. In these technologies a latent, electrostatic image is produced by forming an electrostatic charge on the surface of a photoconductive component (e.g. a drum) and partially or fully discharging the electrostatic charge on parts of the surface of the photoconductive component by exposing those parts to light.. The exposure may be from light reflected from an illuminated image (as in photocopying) or from a laser which scans the photoconductive component, usually under instruction from a computer (as in laser printing). Once a latent image has been produced in charge it is developed, using a toner, to form a visible toner image on the photoconductive component which can then be transferred onto a suitable substrate (e.g. paper) so that a hard copy of the image is obtained after fixing the toner to the substrate. During printing, friction between particles of toner, with their carrier and/or with parts of the electrophotographic apparatus cause the toner particles to obtain an electrostatic charge (tribocharge) which enables them to develop the latent, electrostatic image. The toner may be employed without a magnetic carrier as so-called "one- component" or "mono-component" developer or the toner may be employed with a magnetic carrier as so-called "two component" or "dual-component" developer.

Toner comprises toner particles typically of average particle size 1-50μm but more usually 2-15μm. The toner particles typically comprise a binder resin, a colorant and optionally other components such as, for example, wax, lubricant and/or charge control agent to improve the properties of the toner. The resin acts to fix the toner to the substrate, usually by fusion of the resin onto the substrate by heating. The colorant, which is usually a pigment, imparts the required colour to the toner.

Toners typically also comprise surface additives mixed with the toner particles to modify properties such as, for example, toner flowability, toner durability, toner chargeability, toner cleanability, toner usage and/or toner transfer efficiency which, in turn, may improve the quality of the final image (i.e. print quality). Surface additives are particulate materials of smaller average particle size than the toner particles. For example, the surface additives typically have an average primary particle size in the range 1 to 1000 nanometres (nm). The surface additives may comprise organic and/or inorganic particles but typically comprise inorganic particles. However, there still remains room for improvement in toner properties.

CONFIRMATION COFY In particular it is highly desirable that toners are able to work effectively during and after extensive print runs (for example print runs extending over thousands of prints). We have found that known toners tend to suffer from one or more of the following problems after thousands of prints: i) increased toner wastage and decreased toner usage efficiency; ii) reduced print quality; iii) toner filming on printer components, especially toner filming on the developer roller. The present invention provides a toner which addresses, at least in part, one or more of the abovementioned technical problems. The invention is defined in more detail below.

In one aspect, the present invention provides a toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A of average primary particle size not greater than 10nm; ii) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and iii) a surface additive C of average primary particle size greater than 30nm; wherein the surface additives A, B and C each comprise a silica. It has surprisingly been found that the combination of the three types of surface additive A, B and C, can significantly improve properties of a toner and/or final image formed in an electrophotographic method.

In another aspect, the present invention provides a process for preparing a toner comprising toner particles and surface additives, the process comprising mixing toner particles with: a) a surface additive A of average primary particle size not greater than 10nm; b) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and c) a surface additive C of average primary particle size greater than

30nm; wherein the surface additives A, B and C each comprise a silica.

In still another aspect, the present invention provides the use of the toner according to the present invention in an electrophotographic image forming method.

In a further aspect, the present invention provides an image forming method comprising the steps of: forming an electrostatic image on a photoconductive member; developing the electrostatic image with a toner to form a toner image; transferring the toner image onto a transfer material (e.g. paper); and fixing the toner image onto the transfer material; wherein the toner is a toner according to the present invention.

The surface additives A, B and C and optionally other surface additives may partially or completely coat the surfaces of the toner particles. As described above the surface additives A, B and C must each comprise a silica. To put it otherwise surface additive A comprises silica as does surface additive B and C. Preferably, at least 50%, more preferably at least 75% by weight of each surface additive A, B and C is silica.

In one embodiment each surface additive may independently optionally comprise silica and an inorganic material other than silica. Preferably, the inorganic material other than silica is a metal oxide. Examples of suitable metal oxides include titanium, aluminium and zirconium oxides. Surface additives of this type are available from Degussa, for example mixed silica - aluminium oxide surface additives are available under the tradenames Aerosil MOX™ 80 and 170 and COK™ 84.

Most preferably, each surface additive A, B and C is a silica.

Suitable silicas are commercially available. For example, the following

HDK™ series of silicas marketed by Wacker may be suitable for use with the toner of the present invention: HDK™ H2015EP, H2050EP, H2000T, H3004, H2150VP, H3050VP, H1018, H1303VP, H05TD, H13TD, H20TD, H30TD, H05TM, H13TM,

H20TM, H30TM, H05TX, H13TX, H20TX, H30TX, H05TA, H13TA, H30TA.

Examples of the surface additive A include the silicas R812 and R812S from Degussa; and HDK™ H30TM and H30TX from Wacker.

Examples of the surface additive B include the silicas R972 from Degussa and HDK™ H13TM, H13TX and H15 from Wacker.

Examples of the surface additive C include the silicas RX50 and RY50 from Degussa and HDK™ H05TM and H05TX from Wacker.

Preferably, the surface additive C is of average primary particle size not greater than 60nm, more preferably not greater than about 50nm. The average primary particle size of surface additive C is especially about 50nm.

Each additive A, B and C independently may be present in an amount 0.1 to 5.0 weight %, preferably 0.1 to 3.0 weight % and more preferably 0.2 to 2.0 weight %. The weight % of the additives referred to herein is calculated as a percentage (%) of the weight of the toner particles (i.e. the weight of the toner prior to addition of the surface additives).

In embodiments, most preferably the surface additive A is present in an amount 0.4 to 2.0 weight % (especially 0.5 to 1.8 weight %); the surface additive B is present in an amount 0.1 to 1.5 weight % (especially 0.2 to 1.2 weight %); and the surface additive C is present in an amount 0.1 to 1.5 weight % (especially 0.2 to 1.5 weight %). Preferably, the total (i.e. combined) amount of the additives A, B and C present is 0.5 to 5.0 weight %, more preferably 1.0 to 3.0 weight %, still more preferably 1.5 to 3.0 weight %, especially 2.0 to 3.0 weight %.

In addition to the surface additives A, B and C one or more optional further surface additives may be present.

For example, there may optionally be a fourth surface additive D which is preferably a metal oxide. Suitable optional metal oxides for surface additive D include aluminium, tin, zirconium, zinc, vanadium, iron, magnesium, calcium, barium, gallium, lanthanum, tantalum, cerium oxides and especially titania (titanium oxide).

Preferably, surface additive D is present in an amount 0.1 to 0.5 weight % (especially 0.1 to 0.3 weight %). Preferably, surface additive D has an average primary particle size from 10 to 30nm.

The Table below shows examples of different formulations of the additives A₁ B, C and optionally D which may be used (all amounts in weight %).

In view of the above, it can be seen that in a particularly preferred embodiment of the present invention there is provided a toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A which is or comprises a silica of average primary particle size not greater than 10nm in an amount 0.2 to 2.0 weight %; ii) a surface additive B which is or comprises a silica of average primary particle size greater than 10nm but not greater than 30nm in an amount 0.2 to 2.0 weight %; and iii) a surface additive C which is or comprises a silica of average primary particle size greater than 30nm in an amount 0.2 to 2.0 weight %. Most preferably A, B and C are each a silica. Preferably, the total combined amount of the additives A, B and C present is 0.5 to 5.0 weight %, more preferably 1.0 to 3.0 weight %, calculated as a percentage of the weight of the toner. In more particularly preferred embodiments, there is provided a toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A which is or comprises a silica of average primary particle size not greater than 10nm in an amount 0.4 to 2.0 weight %

(especially 0.5 to 1.8 weight %);

ii) a surface additive B which is or comprises a silica of average primary particle size greater than 10nm but not greater than 30nm in an amount 0.2 to 1.2 weight %; and

iii) a surface additive C which is or comprises a silica of average primary particle size greater than 30nm in an amount 0.2 to 1.5 weight %. Preferably, the surface additives A, B and C are each a silica. The surface additives of the present invention may each independently be either hydrophilic or hydrophobic. However, preferably, at least one, more preferably all, of the surface additives A, B and C is/are hydrophobic. Methods for rendering the surface additives hydrophobic (hydrophobising treatments) are known to the person skilled in the art.

Preferably, all the surface additives A, B and C are hydrophobic. The hydrophobic silica may be formed by reacting silica with one or more organosilicon compounds such as, for example, a silane, silyl amine (including a silazane) and/or siloxane, preferably a silane and/or silyl amine (especially a silazane). The term silane herein includes alkyl silanes, halosilanes, alkylhalosilanes, alkoxy silanes, alkyl alkoxy silanes, haloalkoxysilanes and other substituted silanes). Various reaction conditions known in the art may be used. For example, a fumed silica may be reacted with a gaseous organosilicon compound at elevated temperature. General methods are described, for example, in GB 1 ,031 ,764 and US 4,503,092 (Degussa). Additionally, also known are methods that involve reaction of a fumed silica with a liquid phase organosilicon compound. General methods are described, for example, in US 5,686,054 (Wacker) (and references therein).

Suitable organosilicon compounds for hydrophobising silica, include without limitation: silyl amines (including silazanes such as hexamethyldisilazane ([CHa)₃Si]₂NH) and cyclic silazanes); alkylsilanes such as trimethylsilane; alkylhalosilanes such as methyltrichlorosilane, dimethyldichlorosilane and octylmethyldichlorosilane; vinyl halosilanes such as vinyltrichlorosilane; alkylalkoxysilanes such as dimethyldimethoxysilane, butyl trimethoxysilane, iso- butyl trimethoxysilane and octyl trimethoxysilane; arylhalosilanes; and/or siloxanes such as polysiloxanes containing a repeat unit -(R₂SiO)- where R is an organic group (preferably R is alkyl, more preferably Ci_-4 alkyl, most preferably methyl), examples of polysiloxanes including polydimethylsiloxane and octamethylcyclotetrasiloxane. One, two or more organosilicon compounds may be used for hydrophobising the silica and/or other additives. The abovementioned organosilicon compounds are suitable for producing negatively chargeable hydrophobic silica. A positively chargeable hydrophobic silica may be produced, for example, by including a nitrogen atom in the organosilicon compound (preferably in the form of an amino or ammonium group) so that the silica becomes functionalised with a nitrogen containing group (preferably an amino or ammonium group). Preferably, the silica for use in the present invention is negatively charging. Accordingly, preferably the toner of the present invention is negatively charging.

Examples of hydrophobic silicas include those commercially available from Nippon Aerosil, Degussa, Wacker and Cabot Corporation. Specific examples include those made by reaction with dimethyldichlorosilane (e.g. Aerosil™ R972 and R974 from Degussa and H30 and H15 from Wacker); those made by reaction with polydimethylsiloxane (e.g. Aerosil™ RY50, NY50, RY200, RY200S and R202 from Degussa); those made by reaction with hexamethyldisilazane (e.g. Aerosil™ RX50, NAX50, RX200, RX300, R812 and R812S from Degussa and HDK™ H30TM, H13TM and H05TM from Wacker); those made by reaction with alkyl silanes (e.g. Aerosil™ R805 and R816 from Degussa) and those made by reaction with octamethylcyclotetrasiloxane (e.g. Aerosil™ R104 and R106 from Degussa).

Preferably, the optional surface additive D is selected from the group consisting of titania and alumina. Preferably, surface additive D is hydrophobic. Surface additive D may be hydrophobized by the same synthetic methods described above for silica. When optional surface additive D is titania it is preferably titania which has been hydrophobised, e.g. by reaction with an alkyl silane and/or a polysiloxane. The titania may be crystalline or amorphous. Where crystalline it may consist of rutile or anatase structures, or mixtures of the two. Examples of suitable titania include grades T805 or NKT90 from Nippon Aerosil. When optional surface additive D is alumina (alumium oxide) it may be hydrophilic or hydrophobic.

Hydrophilic alumina is a preferred alumina. A preferred grade is Aluminium Oxide C from Degussa.

In especially preferred embodiments of the present invention, the additive A is a silica which is hydrophobised. More preferably, the additive A is a silica which is hydrophobised by reaction of silica with a silyl amine, more preferably a silazane and especially hexamethyldisilazane (e.g. R812 and R812S from Degussa and HDK™ H30TM from Wacker).

In especially preferred embodiments of the present invention, the additive B is a silica which is hydrophobised. More preferably, the additive B is a silica which is hydrophobised by reaction of silica with a silyl amine, more preferably a silazane and especially hexamethyldisilazane (e.g. HDK™ H13TM from Wacker), polydimethylsiloxane (e.g. HDK™ H15TD from Wacker) or a combination of a silyl amine (more preferably a silazane and especially hexamethyldisilazane) and polydimethylsiloxane (e.g. HDK™ H13TX from Wacker). Even more preferably, the additive B is a silica which is hydrophobised by reaction of silica with hexamethyldisilazane.

In especially preferred embodiments of the present invention, the additive C is a silica which is hydrophobised. More preferably, the additive C is a silica which is hydrophobised by reaction of silica with a silyl amine, more preferably a silazane and especially hexamethyldisilazane (e.g. HDK™ H05TM from Wacker).

Accordingly, in embodiments, the present invention provides a toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A of average primary particle size not greater than 10nm; ii) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and iii) a surface additive C of average primary particle size greater than 30nm; wherein surface additives A, B and C are each a silica which has been hydrophobised by reaction with a silyl amine, more preferably a silazane and especially hexamethyldisilazane. Optionally, one or more of the surface additives may have been hydrophobised by reaction with a further hydrophobising agent in addition to hexamethyldisilazane, e.g. a polysiloxane such as polydimethylsiloxane. Examples of such a silica include H13TX available from Wacker. However, preferably, each silica is hydrophobised by reaction with a silyl amine, more preferably a silazane and especially hexamethyldisilazane, alone.

Preferably the carbon content of the hydrophobised surface additives is not greater than about 10 % by weight, more preferably not greater than about 6 % by weight.

Preferably, the hydrophobised silica has about 1 Si-OH group per nm² or less. Highly hydrophobic silica has about 0.5 Si-OH group per nm² or less. In contrast, hydrophilic silica typically has about 2 Si-OH group per nm².

The silica is preferably so-called fumed silica, i.e. which has been formed by the well known flame hydrolysis process, e.g., in which, a silane (e.g. a halosilane such as trichlorosilane or tetrachlorosilane) is introduced into a hydrogen/oxygen flame to produce the fumed silica, which may then be subjected to hydrophobisation treatment as described above. Silica useful in the present invention may be crystalline or amorphous, but is preferably amorphous. Preferably, all the silicas present are fumed silicas.

Optionally, the toner particles may be mixed with one or more further surface additives, i.e. in addition to surface additives A, B and C. For example a further surface additive D may be used. Preferably, the average primary particle size of the one or more further surface additives is from 5 to 50nm, more preferably 10 to 50nm and most preferably 10 to 30nm.

The one or more further surface additives may comprise any surface additive suitable for use with toners. The further surface additives may be an organic particulate material or an inorganic particulate material or a mixture thereof. Examples of organic particulate materials include: polymeric particles or beads, preferably wherein the polymer comprises one or more of acrylic ester polymer, methacrylic ester polymer, polyester and polystyrene and co-polymers thereof; and metal salts of fatty acids, including, for instance, metal stearates (e.g. zinc stearate).

Examples of inorganic particulate materials can be selected, without limitation, from: inorganic oxides, including oxides of silicon and oxides of metals such as titanium, aluminium, tin, zirconium, zinc, vanadium, iron, magnesium, calcium, barium, gallium, lanthanum, tantalum, cerium and/or other metals as well as mixed oxides of any two or more of the foregoing; inorganic carbides, including carbides of silicon and/or titanium; inorganic titanates, including titanates of barium, calcium, strontium and/or lead; inorganic nitrides including boron nitride; carbonates, including carbonates of calcium; and carbon black. Preferably, the one or more further surface additives comprise one or more inorganic oxides, especially selected from silica, titania and alumina. More preferably, the one or more further surface additives comprises one or more metal oxides, especially selected from titania and alumina. Most preferably, the one or more further surface additives comprise titania. A preferred titania is hydrophobic titania, e.g. which has been hydrophobised by reacting the titania with a silane and/or polysiloxane. A preferred titania has an average particle size of 10 to 50nm, more preferably 10 to 30nm.

The primary particles of many surface additives suitable for use in the present invention, especially fumed silicas, may be present as aggregates (i.e. larger collections of primary particles). The size of the aggregates typically may be 50 to 1000nm. Preferred additives for use in the present invention are those in which the primary particles are typically present as aggregates. The terms primary particle size and aggregate as used herein are defined in DIN 53206 (08/72).

The BET surface area of the surface additives used in the present invention preferably may be from 20 to 500m²/g, more preferably 30 to 350m²/g. In the process for making the toner, the toner particles are mixed with the surface additives A, B and C preferably thereby at least partially coating the toner particles with the surface additives.

Known processes for mixing surface additives with toner particles may be employed to mix the surface additives and toner particles according to the present invention.

The surface additives are mixed with the toner particles in the process with suitable energy. The mixing may be performed using any suitable mixing apparatus. Suitable types of mixing apparatus include, for example, impact or shear mixers. High speed impact or shear mixers are preferred. Examples of high speed impact or shear mixers include, for example and without limitation, a Henschel™ type mixer or a Cyclomix™ type mixer. Specific examples of suitable mixing apparatus include, without limitation, a Henschel™ type mixer, a Cyclomix™ type mixer (available from Hosokawa), a Mechanofusion™ type mixer (available from Hosokawa) or a Hybridiser™ type mixer (available from Nara). Preferred apparatus are high speed impact or shear mixers, e.g. a Henschel™ type mixer or a Cyclomix™ type mixer.

The mixing apparatus preferably comprises a fixed member (e.g. a container for the toner particles and surface additives) and at least one rotatable mixing member which rotates in use relative to the fixed member to provide energy for mixing the toner particles and surface additives. The mixer may comprise one rotatable mixing member or a plurality of rotatable mixing members. The fixed member preferably provides a wall of the mixer, e.g. in preferred embodiments the fixed member comprises a container for the toner particles and surface additives which provides a wall of the mixer. The rotatable mixing member is preferably capable of high speed rotation. The rotatable mixing member is preferably mounted on a rotatable shaft located, e.g. centrally, within the fixed member (e.g. container). The rotatable mixing member may take one of many forms, e.g. any of those known in the art. The rotatable member may be in the form of a rotatable mixing arm. The rotatable mixing arm may, for instance, be in the form of a vane, blade, paddle or the like. Examples of such mixers include, for example and without limitation, a Henschel™ type mixer or a Cyclomix™ type mixer. The mixing is preferably performed at room temperature (10-30⁰C), cooling may be required to maintain this temperature despite the generation of heat from friction occurring during mixing.

The energy provided in the mixing step is preferably sufficient to cause the surface additives to at least partially coat the toner particles.

It is possible to mix the different sized additives A, B and C with the toner particles in a single mixing step or a plurality of steps. In the latter case, the smallest additive A may be mixed with the toner particles before, at the same time as, or after the larger additives B and C are mixed. The additives B and C may be mixed with the toner particles in a single step together or they may each be mixed with the toner particles in separate steps. The toner particles are preferably mixed with the additive A in a first step followed by mixing with the additives B and C in a second step.

The toner of the present invention is preferably a non-magnetic toner. Preferably, the toner contains no magnetic material for example magnetite.

The toner particles may have a volume average particle size (d_v) of 1 to 50μm. Preferably, the toner particles have a volume average particle size (d_v) of 3 to 15μm, more preferably 4 to 10μm, and most preferably 5 to 9μm.

Preferably, the toner particles have a GSD_n value which is not greater than 1.40, more preferably not greater than 1.35 and most preferably not greater than 1.30. The GSD_n value is defined by the following expression:

wherein D₅₀ is the particle size below which 50% by number of the toner particles have their size and Di₅₉ is the particle size below which 15.9% by number of the toner particles have their size. Preferably, the toner particles have a GSD_V value which is not greater than

1.35 and most preferably not greater than 1.30. The GSD_V value is defined by the following expression:

wherein D₈₄ I is the particle size below which 84.1 % by volume of the toner particles have their size and D₅₀ is the particle size below which 50% by volume of the toner particles have their size.

Low GSD_n and GSD_V values provide, among other things, toners possessing a more uniform charge distribution leading to improved image quality and which have a lower tendency toward filming.

The volume average particle size (d_v), GSD_n and GSD_V values of the toner are measured by a Coulter™ counter utilising a 100μm aperture. For example, a Coulter™ Multisizer III instrument may be used for this purpose.

The toner particles comprise binder resin and colorant. The toner particles may also comprise wax and/or charge control agent (CCA) and/or one or more other ingredients suitable for use in toners.

The binder resin may comprise a polymer component made by polymerising one or more of the following preferred monomers, styrene and substituted styrenes; acrylate and methacrylate alkyl esters (e.g. methyl acrylate or methacrylate, ethyl acrylate or methacrylate, butyl acrylate or methacrylate, octyl acrylate or methacrylate, dodecyl acrylate or methacrylate etc.); acrylate or methacrylate esters with polar functionality, for example hydroxy or carboxylic acid functionality, hydroxy functionality being preferred (particularly 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, or hydroxy-terminated poly(ethylene oxide) acrylates or methacrylates, or hydroxy-terminated polypropylene oxide) acrylates or methacrylates), examples of monomers with carboxylic acid functionality including acrylic acid and beta-carboxyethylacrylate; vinyl type monomers such as ethylene, propylene, butylene, isoprene and butadiene; vinyl esters such as vinyl acetate; other monomers such as acrylonitrile, maleic anhydride, vinyl ethers etc. Preferably, the polymer is a copolymer.

The binder resin preferably comprises a co-polymer obtained by polymerising two or more of the above monomers. The binder resin may comprise a blend (i.e. mixture) of polymers.

A more preferred binder resin comprises a copolymer of (i) a styrene or substituted styrene, (ii) at least one alkyl acrylate or methacrylate and (iii) a polar- functional (especially hydroxy-functional) acrylate or methacrylate.

Polymers for use as the binder resin may be made by polymerisation processes known in the art, preferably by emulsion polymerisation. However, the binder resin may comprise a component selected from the following list, which are not made by emulsion polymerisation: polyesters, polyurethanes, hydrocarbon polymers, silicone polymers, polyamides, epoxy resins etc. A polyester is preferred among these.

The binder resin may comprise a single polymer but preferably comprises a blend of two or more polymers. When the binder resin comprises a blend of two or more polymers, the two or more polymers are preferably of differing molecular weight.

The molecular weight of the polymer(s) in the binder resin can be controlled by use of a chain transfer agent (e.g. a mercaptan), by control of initiator concentration and/or by heating time. Preferably, the binder resin is prepared from at least one polymer with monomodal molecular weight distribution and at least one polymer with bimodal molecular weight distribution. By a polymer with a monomodal molecular weight distribution we mean one in which the gpc spectrum shows only one peak. By a polymer with a bimodal molecular weight distribution we mean one where the gpc spectrum shows two peaks, or a peak and a shoulder. Polymers with a bimodal molecular weight distribution may be made using a two-stage polymerisation. Preferably a higher molecular weight polymer is made in a first stage, then in a second stage, a lower molecular weight polymer is made in the presence of the first resin. As a result, a bimodal molecular weight distribution polymer is made containing both low and high molecular weight polymers. This may then be mixed with a monomodal low molecular weight polymer in the preferred embodiment.

In a further embodiment of the invention, three polymers can be used, where preferably at least two of these show bimodal molecular weight distributions. In a further preference, the second bimodal polymer is of higher molecular weight than the first.

Preferably, the monomodal molecular weight polymer is a low molecular weight polymer and has a number average molecular weight of from 3000 to 10000, more preferably from 3000 to 6000. Where the binder resin comprises one bimodal polymer and the monomodal polymer, the bimodal polymer preferably has a weight average molecular weight of from 100,000 to 500,000, more preferably from 200,000 to 400,000.

Where the binder resin comprises more than one bimodal polymer and the monomodal polymer, one bimodal polymer may optionally have a weight average molecular weight from 500,000 to 1 ,000,000 or more and another bimodal polymer has a weight average molecular weight of from 100,000 to 500,000.

It is preferred that the overall molecular weight distribution of the toner binder resin shows Mw/Mn of 3 or more, more preferably 5 or more, most preferably 10 or more.

Preferably, the Tg of the binder resin, and more preferably of the or each polymer in the binder resin, is from 30 to 100⁰C, more preferably from 45 to 75°C, most preferably from 50 to 70⁰C. If the Tg is too low, the storage stability of the toner will be reduced. If the Tg is too high, the melt viscosity of the binder resin will be raised, which will increase the fixation temperature and the temperature required to achieve adequate transparency. In the case where the binder resin contains two or more polymers, it is preferred that all the components in the binder resin have a substantially similar Tg.

Higher molecular weight polymers which may be used in the binder resin may also contain cross-linked material by inclusion of a multifunctional monomer (e.g. divinylbenzene or a multi-functional acrylate) in the polymerisation reaction.

The toner particles may be coloured toner particles (e.g. yellow, magenta and cyan) or may be black or white toner particles. Accordingly, the colorant of the toner particles may be of any colour or black or white. The colorant is preferably present in an amount which constitutes 1-15% by weight of the toner particles (i.e. the toner particles prior to any blending with a surface additive), more preferably 1.5-10% and most preferably 2-8wt%. These ranges are most applicable for organic, non-magnetic pigments. If, for example, magnetite was used as a magnetic filler/pigment, the level would typically be higher. The present toner is preferably non-magnetic. The colorant may comprise a pigment or dye. Preferably, the colorant comprises a pigment. Pigments or dyes suitable for use in toners are known in the art. Any suitable pigment or dye can be used, including black and magnetic pigments. For example pigments such as carbon black, magnetite, copper phthalocyanine, quinacridones, xanthenes, mono- and dis-azo pigments, naphthols etc. may be used. Specific examples include Pigment Blue 15:3, Pigment Red 31 , 57, 81 , 122, 146, 147, 184 or 185; and Pigment Yellow 12, 13, 17, 74, 155, 180 or 185. In full colour printing it is normal to use yellow, magenta, cyan and black toners. However, it is possible to make specific coloured toners for spot colour or custom colour applications. Thus, the toner particles of the present invention may comprise, without limitation, yellow, magenta, cyan or black toner particles.

The toner particles preferably comprise wax. Suitable wax should have a melting point (mpt) (as measured by the peak position by differential scanning calorimetry (dsc)) of from 50 to 15O⁰C, preferably from 50 to 13O⁰C, more preferably from 50 to 110⁰C, especially from 65 to 85°C. If the mpt is >150°C the release properties of the toner at lower temperatures are inferior, especially where high print densities are used. If the mpt is <50°C the storage stability of the toner will suffer and the toner may be more prone to showing filming of the photoconductive member or a metering blade.

The wax may be of any kind suitable for use in toners. Examples include hydrocarbon waxes (e.g. polyethylenes such as Polywax™ 400, 500, 600, 655, 725, 850, 1000, 2000 and 3000 from Baker Petrolite and polypropylenes; paraffin waxes and waxes made from CO and H₂, especially Fischer-Tropsch waxes such as Paraflint™ C80 and H1 from Sasol); ester waxes, including natural waxes such as Carnauba and Montan waxes; amide waxes; and mixtures of these. Hydrocarbon waxes are preferred, especially Fischer-Tropsch and paraffin waxes. It is especially preferred to use a mixture of Fischer-Tropsch and Carnauba waxes, or a mixture of paraffin and Carnauba waxes. Functional waxes, i.e. having functional groups, may also be used (e.g. acid functional waxes, such as those made using acidic monomers, e.g. ethylene/acrylic acid co-polymer, or grafted waxes having acid groups grafted onto the wax). Functional waxes may be preferred for compatibility with a polar binder resin, e.g. polyester resin. Mixtures of functional wax with hydrocarbon wax may be used wherein the functional wax acts as a compatibiliser.

The amount of wax incorporated in the toner particles is preferably such that it constitutes from 1 to 30% by weight of the toner particles (i.e. the toner particles prior to any blending with a surface additive), more preferably 2 to 20%, even more preferably from 3 to 20%, especially from 3 to 15% and most especially from 3 to 12%. It is also preferred that wax is substantially not present at the surface of the toner particles.

The toner particles as described above may optionally comprise a charge control agent (CCA). Suitable charge control agents are preferably colourless. Preferably, they include metal complexes, more preferably aluminium or zinc complexes, phenolic resins etc. Examples include Bontron™ E84, E88, E89 and F21 from Orient; Kayacharge N1 , N3 and N4 from Nippon Kayaku; LR147 from Japan Carlit; TN-105 from Hodogaya.

The toner particles may have a shape, defined by shape factors SF1 and SF2, wherein, preferably, SF1 is 100-165 and SF2 is 100-155.

The shape factor, SF1 , is defined as:

SF1 = (ML)²/A x π/4 x100, where ML = maximum length across toner particle, A = projected area of the toner particle

The shape factor, SF2, is defined as: SF2 = P²/A x 1/4π x 100, where P = the perimeter of the toner particle, A = projected area of the toner particle

An average of approximately 100 particles is taken to define the shape factors for the toner.

The toner particles may be made by any methods known in the art. One known process for making toner particles, which may be referred to as a "physical" process, involves taking the binder resin, colorant and optional other internal ingredient(s) and kneading them together in a molten state to mix them. The resultant melt is then cooled, extruded and physically broken down into toner particles by mechanical force, e.g. by a milling process. Typically, the toner particles produced in this way have an average particle size below 20μm. However, the distribution of particle sizes of the toner is often considered to be too wide and, in such cases, a classification step is typically performed to reduce the proportion of toner particles which are too small or too large.

Other, more preferred, processes for making toner particles are known, which may be referred to as "chemical" processes, in which toner particles are formed in a liquid dispersion medium. Toner particles may be formed in a liquid dispersion medium, e.g. from smaller ingredient particles by processes such as, for example, aggregation. In aggregation processes, typically, dispersed resin particles (and preferably colorant particles and optionally particles of other ingredients such as a release agent) are associated to form larger, aggregate particles, which are useful as toner particles, optionally after further treatment such as heat treatment to fuse and/or shape the aggregate particles. Examples of aggregation processes include those processes described in US 4,983,488, US 4,996,127, EP 631196 and WO 98/50828 the contents of which are hereby incorporated by reference. Another type of chemical process in which toner particles are formed is suspension polymerisation. An example of a process in which toner particles are formed by suspension polymerisation is described in US 4,592,990.

Before use in electrophotography, the toner formed in a chemical process must be dried to remove the majority of liquid (e.g. water) from the toner. The toner particles are preferably dried before mixing with the surface additives of the present invention.

Chemical processes for producing toners provide a greater degree of control of the properties of resultant toner particles such as average particle size, particle size distribution, particle shape and/or particle composition. In particular, toners prepared by chemical processes have a narrower particle size distribution than toners made by a physical process such that a classification step is often not required. The toner particles of the present invention are preferably made by a chemical process, more preferably by an aggregation process and especially a process as described in WO 98/50828 and WO 03/087949, the content of which is hereby incorporated by reference.

In embodiments, the toner particles are preferably made by a process which comprises providing a dispersion containing primary resin particles, primary colorant particles and optionally primary wax particles and causing the particles in the dispersion to associate. The associated particles preferably form aggregate particles which comprise the primary resin, colorant and optionally wax particles. The aggregate particles are preferably then fused by heating (preferably above the glass transition temperature (Tg) of the resin particles) to form toner particles.

In more preferred embodiments, the toner particles are preferably made by a process which comprises the steps of: a) providing a latex dispersion containing primary resin particles and surfactant; b) providing a colorant dispersion containing primary colorant particles and surfactant; c) optionally providing a wax dispersion containing primary wax particles and surfactant; d) mixing the latex dispersion, colorant dispersion and optional wax dispersion; and e) causing the particles in the mixture formed in (d) to associate. The latex dispersion contains primary resin particles which are particles of the binder resin which goes to make up the bulk of the toner particles. Preferably, the latex dispersion is a dispersion of the resin particles in water. The latex dispersion preferably comprises an ionic surfactant to stabilise the resin particles in dispersion. Optionally, a non-ionic surfactant may also be incorporated into the latex dispersion. The latex dispersion may be prepared by suitable polymerisation processes for example those currently known in the art, preferably, but not necessarily, by emulsion polymerisation. The average size of the primary resin particles in the latex dispersion, as measured using photon correlation spectroscopy, is preferably no more than 200nm (e.g. 40-200nm) and more preferably no more than 150nm (e.g. 40-150nm). The average size of the primary resin particles may, for example lie in the range 80-120nm.

Preferably, the colorant dispersion is a dispersion in water. The colorant dispersion may be prepared by any suitable processes for example those currently known in the art, preferably by milling the colorant with a surfactant in an aqueous medium. The colorant dispersion preferably comprises an ionic surfactant to stabilise the colorant particles in the dispersion. Optionally, a non-ionic surfactant may also be incorporated into the colorant dispersion. Preferably, the volume average size of the primary colorant particle, which may be measured by a light scattering method, is less than 300nm, more preferably less than 200nm and most preferably less than 10Onm.

Preferably, a wax dispersion is used in the process. The wax dispersion is preferably a dispersion in water. The wax dispersion is preferably prepared by the mixing together of a wax with an ionic surfactant to stabilise the wax particles in the dispersion. The volume average particle size of the primary wax particles, which may be measured by a light scattering method, in the dispersion is preferably in the range from 100nm to 2μm, more preferably from 100 to 800nm, still more preferably from 150 to 600nm, and especially from 200 to 500nm. The wax particle size is chosen such that an even and consistent incorporation into the toner is achieved. The process for preparing toner particles may further comprise providing a charge control agent (CCA). The CCA may be provided as a component of one of the dispersion in steps (a) - (c) or the CCA may be provided separately and added as part of the pre-association mixture, preferably as a solution or wet cake.

The particles in the mixture obtained in step (d) may be caused to associate in step (e) by any suitable method. For instance, the association may be caused by heating and stirring as described, for example, in US 4,996,127, by the addition of an inorganic salt as described, for example, in US 4,983,488 or by the action of organic coagulants, including counterionic surfactants as described, for example, in US 5,418,108. In a preferred method, the association is caused by a pH switch, i.e. by effecting a change in the pH, preferably either from a basic pH to an acidic pH or from an acidic pH to a basic pH. Such association processes are described in WO 98/50828, WO 99/50714 and WO 03/087949. In a pH switch process, the latex dispersion, colorant dispersion and optional wax dispersion are each stabilised with an ionic surfactant of the same sign which is capable of being converted from an ionic to a non-ionic form (and vice versa) by a change in pH (i.e. each surfactant is reversibly ionisable or de-ionisable). Preferably, the same surfactant is employed to stabilise the latex dispersion, colorant dispersion and optional wax dispersion. In a particularly preferred example, the surfactant may contain a carboxylic acid group, and the dispersions may be mixed at neutral to high (i.e. above neutral) pH with association then being effected by addition of an acid, which decreases the pH and converts the surfactant from its dispersion stabilising anionic form to its less-stabilising non-ionic form. Alternatively, in another preferred example, the surfactant may contain a group which is the acid salt of a tertiary amine, and the dispersions may be mixed at neutral to low (i.e. below neutral) pH with association then being effected by addition of a base which increases the pH and converts the surfactant from its dispersion stabilising cationic form to its less-stabilising non-ionic form.

Stirring and mixing are preferably performed during the association step.

The association step is preferably carried out below the Tg of the resin in the latex.

The associated particles may be collected and used as toner particles. However, preferably, the associated particles are subjected to further treatment.

After the association step (e), the process preferably comprises a further step (f) of heating and/or stirring the associated mixture (preferably at a temperature below the Tg of the resin particles). Preferably such heating and/or stirring of the associated mixture causes loose aggregates to form. The aggregates are composite particles comprising the primary particles of resin, colorant and optionally wax. Preferably, the aggregates are of particle size from 1 to 20μm, more preferably from 2 to 20μm. Once the desired aggregate particle size is established, the aggregates may be stabilised against further growth. This may be achieved, for example, by addition of further surfactant, and/or by a change in pH where a pH switch process was employed for the association as is known in the art (e.g. WO 98/50828).

After the association step (e) and optional further step (f) of heating and/or stirring to establish the desired particle size, the temperature may then be raised above the T₉ of the resin in a step (g) to form toner particles. The step (g) brings about coalescence of the particles, e.g. within each aggregate and/or between aggregates, to form toner particles.

The dispersion of toner particles may then be cooled and the toner particles recovered, e.g. by filtration. The toner may then optionally be washed (e.g. to remove at least some surfactant) and/or optionally be dried using suitable methods to provide dried toner particles for subsequent mixing with the surface additives.

As previously described the toner of the present invention is especially suitable for use in electrophotography. Suitable electrophotographic apparatus (photoconductive members etc.) are well known in the art. Suitable transfer materials (substrates) are well known in the art and include paper and overhead transparencies.

The toner according to the present invention can be used in an electrophotographic (image forming) method on its own as so-called "mono- component" developer or in combination with a carrier, such as a magnetic carrier, as so-called "two component" developer. Suitable carriers are well known in the art. The present invention preferably provides mono-component developer consisting of the toner of the present invention (i.e. the toner not in combination with a magnetic carrier).

The use of the surface additives A, B and C in the present invention has been found to provide a toner capable of forming images of good print quality with good toner usage.

Preferably, the invention provides a toner which may satisfy many other requirements simultaneously. The toner may be particularly advantageous for use in a mono-component electrophotographic apparatus and may be capable of demonstrating: formation of high resolution images; formation of images with good image density; release from fusion rollers over a wide range of fusion temperature and print density; high transparency for OHP slides over a wide range of fusion temperature and print density; high transfer efficiency and the ability to clean any residual toner from the photoconductor, and the absence of filming of the metering blade, development roller and photoconductor over a long print run. The toner of the invention may have good flow properties and/or good chargeability properties and/or good durability. Throughout the description and claims of this specification, the words

"comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components and/or steps.

Unless the context clearly indicates otherwise, plural forms of the terms herein are to be construed as including the singular form and vice versa.

All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to or alternative to any invention presently claimed. Discussion of documents, acts, materials, devices, articles and the like is included herein solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art or were common general knowledge in the field relevant to the present invention as it existed before the priority date or filing date of this patent application.

The invention will now be illustrated by the following Examples, which are non-limiting on the scope of the invention. All percentages or parts referred to are percentages or parts by weight unless otherwise stated.

Examples

1. Preparation of toner particles

Cyan, yellow, magenta and black toners were made by a method similar to that outlined in PCT patent publication WO 03/087949. The latexes used were analogous to those in WO03/087949, for each toner a mixture of three latexes of different molecular weight was used, in order to generate a broad molecular weight distribution. Each latex was made by emulsion polymerisation, using styrene, acrylic ester monomers and 2-hydroxyethyl methacrylate. The pigments used were not those described in WO 03/087949 but were instead Pigment Blue

15:3 for the cyan toner, Pigment Yellow 74 for the yellow toner, Pigment Red 184 for the magenta toner and carbon black for the black toner. The wax and CCA used in these toners were as described in the Examples in WO 03/087949. That is to say, the wax was an 80:20 weight mixture of Paraflint™ C80 (a Fischer-Tropsch wax) from Sasol and Carnauba wax and the CCA was Bontron™ E88 from Orient.

The volume average particle size of the toner particles, as measured with a

Coulter Multisizer, was in the range 8-9μm.

2. 1 Example 1 (Comparative) Each colour of toner particles prepared in point 1 was then mixed with 0.5 weight % (based on the weight of toner particles) of a surface additive A consisting of small size hydrophobic silica (Aerosil R812S from Degussa, average primary particle size 7nm). The toner particles and silica were mixed in a Prism Pilot 3 mixer (Thermo Scientific) for 30 seconds at 500rpm, followed by 30 seconds at 3,000rpm, followed by 3 mins at 5,500rpm. The mixed products were then sieved through a 45μm sieve. The resultant Toners were designated Y1 (yellow toner), M1 (magenta toner) and C1 (cyan toner). 2.2 Example 2 (Comparative)

Each colour of toner particles prepared in point 1 was mixed with 0.5 weight % of a surface additive A consisting of small size hydrophobic silica (Aerosil R812S from Degussa, average primary particle size 7nm) in the manner of Example 1. This was then followed by further mixing with 1.5 weight % of a surface additive B consisting of medium size hydrophobic silica (HDK H13TM from Wacker, average primary particle size 20nm) in a second step for 30 seconds at 500rpm, followed by 3 mins at 5,500rpm. The resultant Toners, after sieving, were designated Y2 (yellow toner), M2 (magenta toner) and C2 (cyan toner).

2.3 Example 3 (Invention)

Each colour of toner particles prepared in point 1 was mixed with 0.5 weight % of a surface additive A consisting of small size hydrophobic silica (Aerosil R812S from Degussa, average primary particle size 7nm) in the manner of Example 1. This was then followed by further mixing with 1.0 weight % of a surface additive B consisting of medium size hydrophobic silica (HDK H13TM from Wacker, average primary particle size 20nm) and 1.3 weight % of a surface additive C consisting of large size hydrophobic silica (HDK H05TM from Wacker, average primary particle size 50nm) in a second step for 30 seconds at 500rpm, followed by 3 mins at 5,500rpm. The resultant Toners, after sieving, were designated Y3 (yellow toner), M3 (magenta toner) and C3 (cyan toner).

3. Testing

The Toners made in Examples 1-3 (points 2.1-2.3) above were evaluated by print testing. Cartridges from a Lexmark C522 printer were filled with 55g of each of the Toners. Then the C522 printer was used to print pages with a bar pattern having a total printing area of 1% paper coverage. At 1000 page intervals, the weight of the cartridge was recorded to assess toner usage and a full colour

A4 page was printed to assess print quality. At the end of the test, the developer roller of the cartridge were also examined to assess whether any filming had occurred.

4. Results

The results of the print quality test are shown in Tables 1A-1C below. Print quality was assessed as 1 , 2 or 3 (1 = Good, 2 = Acceptable, 3 = Poor). The usage (in grams) of the Toners is shown Tables 2A-2C.

The Toners of Example 2 (Comparative) (Y2, M2 and C2) gave no significant overall benefit in print quality compared to the Toners of Example 1 (Comparative) (Y1 , M1 and C1 ) and their toner usage rate was higher when averaged over all four colours. The Toners of Example 3 (Invention) (Y3, M3 and C3) on the other hand gave much better print quality than either Toners of Example 1 or Toners of Example 2. Also, it was seen that the toners of the present invention maintained print quality for more extensive print runs, typically adding the ability to print several thousand more prints having an acceptable or good quality. The Toners of Example 3 also generally gave lower toner usage rates. In addition, no filming could be seen on the developer roller.

Tables 1 A to 1C - Print Quality

(1 = Good, 2 = Acceptable, 3 = Poor)

Table 1 C - Cyan Toners

Tables 2A to 2C - Toner Usage

Table 2A - Yellow Toners

The average toner usages per 1000 prints were: Y1 (Comparative) = 16.Oq, Y2 (Comparative) = 12.1q and Y3 (Invention) = 7.3q.

Table 2B - Ma enta Toners

The average toner usages per 1000 prints were: M1 (Comparative) = 6.3g, M2 (Comparative) = 12.6g and M3 (Invention) = 6.1g.

Table 2C - C an Toners

The average toner usages per 1000 prints were: C1 (Comparative) = 11.5g, C2 (Comparative) = 17.Og and C3 (Invention) = 6.4g.

Claims

1. A toner comprising toner particles and surface additives, the surface additives comprising: i) a surface additive A of average primary particle size not greater than 10nm; ii) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and iii) a surface additive C of average primary particle size greater than 30nm; wherein the surface additives A, B and C each comprise a silica.

2. A toner according to claim 1 wherein each surface additive A, B and C is silica.

3. A toner as claimed in any one preceding claim wherein the surface additive C is of average primary particle size not greater than 60nm.

4. A toner as claimed in any one preceding claim wherein each additive A, B and C independently is present in an amount 0.1 to 3.0 weight %.

5. A toner as claimed in claim 4 wherein each additive A, B and C independently is present in an amount 0.2 to 2.0 weight %.

6. A toner as claimed in any one of claims 1 to 3 wherein the surface additive A is present in an amount 0.4 to 2.0 weight %, the surface additive B is present in an amount 0.1 to 1.5 weight % and the surface additive C is present in an amount 0.1 to 1.5 weight %.

7. A toner as claimed in any one preceding claim wherein the total amount of the additives A, B and C present is 0.5 to 5.0 weight %.

8. A toner as claimed in any one preceding claim wherein the toner comprises one or more further surface additives.

9. A toner as claimed in claim 8 wherein the one or more further surface additives has\have an average primary particle size from 10 to 50nm.

10. A toner as claimed in any one preceding claim wherein the surface additives A, B and C are hydrophobic.

11. A toner as claimed in claim 10 wherein the surface additives A, B and C have been made hydrophobic by reaction with one or more organosilicon compounds.

12. A toner as claimed in claim 11 wherein the one or more organosilicon compounds are selected from the group consisting of silyl amines, alkyl silanes, alkyl halosilanes, alkyl alkoxysilanes, aryl halosilanes and siloxanes.

13. A toner as claimed in claim 12 wherein the surface additives A, B and C have been made hydrophobic by reaction with a silyl amine.

14. A toner as claimed in claim 13 wherein the silyl amine is hexamethyldisilazane.

15. A toner as claimed in any one preceding claim wherein the toner particles have a volume average particle size (d_v) of 4 to 10μm.

16. A toner as claimed in any one preceding claim wherein the toner particles have been made by a chemical process.

17. A toner as claimed in claim 16 wherein the toner particles have been made by a process which comprises providing a dispersion containing primary resin particles, primary colorant particles and optionally primary wax particles, causing the particles in the dispersion to associate to form aggregate particles and fusing the aggregate particles by heating to form toner particles.

18. A toner as claimed in any one preceding claim which is non-magnetic.

19. A process for preparing a toner comprising toner particles and surface additives, the process comprising mixing toner particles with: a) a surface additive A of average primary particle size not greater than 10nm; b) a surface additive B of average primary particle size greater than 10nm but not greater than 30nm; and c) a surface additive C of average primary particle size greater than 30nm; wherein the surface additives A, B and C each comprise a silica.

20. A process according to claim 19 wherein each surface additive A, B and C is silica.

21. Use of the toner according to any one of claims 1 to 18 in an electrophotographic image forming method.

22. An image forming method comprising the steps of: forming an electrostatic image on a photoconductive member; developing the electrostatic image with a toner to form a toner image; transferring the toner image onto a transfer material; and fixing the toner image onto the transfer material; wherein the toner is a toner as claimed in any one of claims 1 to 18.