EP0801333A2

EP0801333A2 - Toner composition

Info

Publication number: EP0801333A2
Application number: EP97200834A
Authority: EP
Inventors: Serge Tavernier; Jean-Pierre Ghekiere; Werner Op De Beeck; Theofiel Stuer
Original assignee: Agfa Gevaert NV
Current assignee: Xeikon Manufacturing NV
Priority date: 1996-04-09
Filing date: 1997-03-20
Publication date: 1997-10-15
Also published as: EP0801333A3; JPH1039539A; JP2996629B2

Abstract

A toner composition is provided comprising toner particles having a BET surface between 0.4 and 1.5 m<2>/g and a melt viscosity between 150 and 2,000 Pa.s at 120 DEG C and n different types of inorganic hydrophobic particles wherein the amount of inorganic particles is chosen such that the total BET surface of the inorganic particles relates to the BET surface of the toner particles in a specific way. In the composition sum of the BET surface of each of the types of inorganic particles multiplied with their respective weight percentage relative to the toner amount relates to the BET surface of the toner particles in a ratio BR, such that 150 ≤ BR ≤ 375. The use of the toner composition in an electrostatographic method wherein the images are fixed in a non-contact fusing step is beneficial for good gloss control.

Description

1. Field of the invention.

The present invention relates to a toner composition suited for development of electrostatic charge images or magnetic patterns and for Direct Electrostatic Printing. It also relates to an electrostatographic method for imaging with a dry toner particles, wherein the toner image is fixed to a final substrate by a non-contact fusing process.

2. Background of the invention

Electrostatic printing methods are manifold, e.g. Direct Electrostatic Printing, wherein electrostatic printing is performed directly from a toner delivery means on a receiving substrate, the latter not bearing any imagewise latent electrostatic image, by means of an electronically addressable printhead structure.
In another form of electrostatic printing toner images are made on an image-forming element in the form of a rotating drum provided with an electrostatic layer built up from a number of controllable electrodes in and beneath a dielectric layer. The voltage that is image-wise applied to said controllable electrodes attracts charged toner particles from a toner source.
It is also well known in the art of electrographic printing and electrophotographic copying to form an electrostatic latent image corresponding to either the original to be copied, or corresponding to digitized data describing an electronically available image.
In electrophotography an electrostatic latent image is formed by the steps of uniformly charging a photoconductive member and imagewise discharging it by an imagewise modulated photo-exposure.
In electrography an electrostatic latent image is formed by imagewise depositing electrically charged particles, e.g. from electron beam or ionized gas onto a dielectric substrate.
The obtained latent images are developed, i.e. converted into visible images by selectively depositing thereon light absorbing particles, called toner particles, which usually are triboelectrically charged.
In toner development of latent electrostatic images two techniques have been applied : "dry" powder and "liquid" dispersion development of which dry powder development is nowadays most frequently used.
The visible image of electrostatically or magnetically attracted toner particles is not permanent and has to be fixed by causing the toner particles to adhere to each other and the substrate by softening or fusing them followed by cooling. Normally fixing proceeds on more or less porous paper by causing or forcing the softened or fused toner mass to penetrate into the surface irregularities of the paper.
Dry-development toners essentially comprise a thermoplastic binder consisting of a thermoplastic resin or mixture of resins (ref. e.g. US-P 4,271,249) including colouring matter, e.g. carbon black or finely dispersed dye pigments. The triboelectrically chargeability is defined by said substances and may be modified with a charge controlling agent. Dry-development toners can be of various types. It can be magnetic toner particles, used as such in a mono-component dry developer, it can also be non-magnetic particles being used as such in a non-magnetic mono-component developer or being mixed with magnetic carrier particles to form a two-(multi-)component dry developer.
In order to have toner compositions wherein the toner particles do not clump together and the composition stays free flowing, the addition of fluidity improvers to the toner composition is widely known in the art. In e.g. US 3,720,617 it is taught to add between 0.01 and 15 % of hydrophobized silica to the toner composition in order to enhance the longevity of the developer and the fluidity of it. It has further been disclosed that the addition of mixtures of powdery inorganic additives in a toner composition can have beneficial effects on the performance of said toner composition.
In US 5,312,711 it is disclosed to add hydrophobized silica, being hydrophobized by a fluor containing silane compound, to a toner composition. By doing so both the fluidity and the uniform chargeability of the toner particles are enhanced.
In EP-A 479 875 it is disclosed to blend hydrophobic silica with small (diameter lower than 7 µm) toner particles wherein the silica is characterised by a product of methanol value (degree of hydrophobicity) and BET surface. The mixing proceeds in such a way that a determined ratio between apparent density and bulk density of the toner composition is reached. The aim of that disclosure is to improve the fluidity of small toner particles.
In, e.g. US 4,623,605 the use of two different types of hydrophobic additives is described, one being hydrophobized silica, the other being hydrophobized titania. The teachings of said application are directed to an electrostatic imaging process wherein the toner particles are fixed upon a final substrate by heat and pressure (by a hot pressure roller). Also in JP-A 62/129866, the use of a silica additive together with non-silica inorganic additives is described in a very general way over a very broad range of concentrations as a way to stabilise positive chargeability in a multi-component developer. It is taught that the concentration of the silica should be smaller than that of the other inorganic additive and that the relative proportion of the silica to the other additive is in the range of 0.01 to 0.50. In US 4,626,487 a mono-component developer (i.e. a developer without magnetic carrier particles) has been disclosed wherein two different types of inorganic particles, one type with a BET surface between 0.2 and 30 m²/g, preferably between 1.0 and 6.0 m²/g and one with a BET surface between 40 and 400 m²/g, are also present. The particles with low BET are preferably hard and are strontium titanate or cerium oxide.
In GB-A 2,222,269 an electrophotographic toner is disclosed containing a colorant and a binder resin also containing fine SiO₂ powder with an average particle size of maximum 0.1 µm and TiO₂ particles with an average size of minimum 0.1 µm. The inorganic particles are adhered on the surface of the toner particles. The use of these toner particles minimises blurring (e.g. poor toning and satellite formation), due to the formation of toner with opposite charge. It can be used with or without a carrier. The fusing in the patent cited proceeds by a hot roller fuser, being a contact fuser.
In US 5,120,631, a fine toner is described, for a full-colour system. A mixture of both a inorganic hydrophobic additive and an inorganic hydrophillic additive is described. From the theory of wetting, it can be expected that the use of a hydrophillic additive in the toner composition will impede proper melting of the hydrophobic binder of the toner and hence good interpenetration during the melt-fixing step, when no additional forces are used, such as in a non-contact fusing process. In the patent cited, the described toner is used in a fusing system using heat and pressure, the electrophotographic device containing a hot roller fusing system.
From the references above it seems that the addition of mixtures of hydrophobic and hydrophillic inorganic additives to toner particles are useful in electrographic systems comprising a fixing step using heat and pressure, but do not bring advantages in systems using non-contact fixing.
One of the quality parameters of an image formed by dry toner particles, among such parameters as resolution, fog, graininess, etc, is the gloss of the final image. Methods for producing toner images using non-contact fusing steps are often preferred, since the drawbacks (hot-offset, addition of silicone oil with detrimental influence on gloss) of hot-roller fixing are avoided. However these also pose problems as the toner resins are to be designed low viscous in behaviour above the softening point of the toner. This implies that the toners have the tendency to interflow very good and to offer rather smooth surfaces, thus giving a rather high gloss. The single layers are conforming to the paper and offer a less smooth image. The bi-, ter- and quadruple layers are however more glossy. Therefore there is apart from a rather glossy appearance the problem of gloss differences depending on thickness.
Means for controlling the gloss of a non-contact fixed toner image have been disclosed in EP-A 656 129, wherein it is disclosed to add to the toner particles compounds that are slightly incompatible with the toner resin or by blending two slightly incompatible polymers and to use that blend as toner resin.
As an other solution to improve the gloss of a toner image, it has been disclosed to apply a layer of colourless toner particles on top of the four colour toner image. Typical examples of such layers and different ways to apply such a layer are disclosed in, e.g., EP-A 629 921, EP-A 486 235, US 5,234,783, US 4,828,950, EP-A 554 981, WO 93/07541 and Xerox Research Disclosure Journal, Vol.16, N^o 1, p. 69 (January/February 1991).
These disclosures have however one property in common, in each of them an additional toner station, to accommodate and deposit the colourless toner particles, is needed in the electrographic apparatus. This complicates the apparatus, slows the process down and raises the cost of the apparatus.
Therefore means and ways to achieve even gloss in a multi-colour toner image without the need of an additional toner station is very desirable. The teachings of EP-A 656 129, cited above, offer a solution to the problem of gloss via the composition of the toner resin that is used in the colour toners. However toner compositions enabling further gloss control are still desirable.

3. Objects and summary of the invention

It is an object of the invention to provide a method for fixing toner images on a final substrate wherein the gloss of the final image is easily controlled.
It is a further object of the invention to provide a toner composition that can be used in electrographic, magnetographic, ionographic imaging method comprising a non-contact fusing step and gives images with even gloss.
It is a still further object of the invention to provide a toner composition providing final images with equal gloss when used in imaging methods using solid toner particles, wherein the toner particles are fixed to a final substrate by radiant heat.
The objects of the invention are realized by providing a toner composition comprising toner particles and number n of different types of hydrophobic inorganic particles, characterised in that

i) said number n is at least 2,
ii) said toner particles comprise a toner resin and have a melt viscosity η such that 150 Pa.s ≤ η ≤ 2,000 Pa.s, measured in a plate/plate rheometer at 120 °C and at 100 rotation/s and an average BET surface (BET_ton) such that 0.4 m²/g ≤ BET_ton ≤ 1.5 m²/g and
iii) said n different types of inorganic particles have each an average BET surface (BET_ip1,...., BET_ipn) and are each present in said toner composition for A₁,...., A_n % by weight (% wt) with respect to the toner particles so that 150 ≤ BR ≤ 375 wherein $BR = \frac{i =1 n (A_{i} x ({BET}_{ip})_{i})}{{BET}_{ton}}$

4. Detailed description of the Invention.

It has been found that the gloss of a toner image fixed on a final substrate by non-contact fusing could be controlled by adjusting the melt-viscosity of the toner particles and by adding hydrophobic inorganic particles in such a way that the total BET surface of the inorganic particles stays in a defined relationship to the BET surface of the toner particles.
It was found that it was beneficial for gloss control, when the toner image was fixed by non-contact fusing, to add a number n of different types of hydrophobic inorganic particles, each having an average BET surface (BET_ip1....BET_ipn), to toner particles, said toner particles having a melt viscosity η such that 150 Pa.s ≤ η ≤ 2,000 Pa.s, measured in a plate/plate rheometer at 120 °C and at 100 rotation/s and having an average BET_ton surface between 0.4 m²/g and 1.5 m²/g, and to add each said number n of different types of hydrophobic inorganic particles in an amount (% by weight with respect to the toner particles) (A₁....A_n) so that 150 ≤ BR ≤ 375 wherein $BR = \frac{i =1 n (A_{i} x ({BET}_{ip})_{i})}{{BET}_{ton}}$
The BET surface of both toner particles and hydrophobic inorganic particles can be measured by a method described by Nielsen and Eggertsen in "Determination of Surface Area Adsorption measurements by continuous Flow Method", Analytical Chemistry, Vol. 30, No. 9 (1958) p. 1387-1390. Toner particles with a BET surface between 0.4 m²/g and 1.5 m²/m are toner particles having an average volume diameter between 10 and 3 µm. BET_ton stands for the BET surface of the toner particles as such.
It was found that the gloss control was even better when 200 ≤ BR ≤ 330.
In a further preferred embodiment the toner particles have a melt viscosity η between 250 and 1,500 Pa.s.
In a still more preferred embodiment, the number n of different types of inorganic hydrophobic particles is 2 and the first type of inorganic hydrophobic particles (IP1) has a BET surface (BET_ip1) larger than the BET surface of the second type of said inorganic particles (BET_ip2) and each of said two types of inorganic hydrophobic particles are present in said toner composition in an amount (A₁, A₂) in % by weight (% wt) with respect tot the toner particles) such that 150 ≤ BR ≤ 375, or more preferred 200 ≤ BR ≤ 330.
In a even more preferred embodiment of the present invention, when two types of hydrophobic inorganic particles are used, each of said two types of inorganic hydrophobic particles are present in said toner composition in an amount (A₁, A₂ in % by weight (% wt) with respect tot the toner particles) such that 0.25 % wt < A₁ + A₂ < 2.5 % wt and 0.4 < A₁/A₂ < 2, moreover it is preferred that BET_ip1 > 150 m²/g and BET_ip2 < 150 m²/g. Most preferably BET_ip1 ≥ 200 m²/g and 30 m²/g < BET_ip2 ≤ 100 m²/g.
In a more preferred embodiment of the invention said two different types of inorganic hydrophobic particles are each present in said toner composition in an amount (A₁, A₂ in % by weight (% wt) with respect tot the toner particles) such that 0.5 % wt < A₁ + A₂ < 1.5 % wt and 0.5 < A₁/A₂ < 1.5. It is preferred that the inorganic hydrophobic particles with the larger BET surface are hydrophobic silica particles and the inorganic hydrophobic particles with the smaller BET surface are hydrophobic titania (TiO₂). The hydrophobic titania is preferably crystalline of the rutile or anatase type.
Suitable hydrophobic silica can be fumed silica as well as precipitated silica. Useful silica, for the instant invention, can be found among the different types of hydrophobic silica marketed by DEGUSSA of Germany under the trade name AEROSIL. Particularly suitable are AEROSIL R812 with BET surface of 260 m²/g, AEROSIL R974 with BET surface of 170 m²/g and AEROSIL R805 with BET surface of 150 m²/g, AEROSIL R202 with BET surface of 100 m²/g and AEROSIL R972 with BET surface of 110 m²/g. Other useful inorganic hydrophobic particles of the silica type, can be precipitated silica particles that are made hydrophobic. Such silica particles are available through NIPPON SILICA of Japan under trade names SILICA SS10, with BET surface of 87 m²/g, SILICA SS20 with BET surface of 113 m²/g, SILICA SS40 with BET surface of 59 m²/g and SILICA SS70 with BET surface of 42 m²/g.
Suitable hydrophobic TiO₂, is, e.g., TITANDIOXID T805 (tradename of DEGUSSA of Germany) with BET surface of 45 m²/g.
It was found that the use of a mixture of two different types of hydrophobic inorganic particles had advantages over the use of only one type. When the amount of said one type of hydrophobic inorganic particles was such that the BR was between 150 and 375 or between 200 and 330, with n = 1, good gloss control was possible, but said hydrophobic inorganic particles had seemingly an strong influence on the charge of the toner particles, since with the use of one type of said inorganic particles no appropriate optical density could be reached at moderate development potentials. It was found that, when in a toner composition according to the present invention two different type of inorganic hydrophobic particles were present, both good gloss control and control of optical density was possible. Even better results in gloss control and in optical density were obtained when as inorganic particles IP1 hydrophobic SiO₂ particles and as inorganic particles IP2 hydrophobic TiO₂ particles where used. The best results were obtained when said hydrophobic TiO₂ particles were crystalline particles of the rutile or anatase type. The toner compositions according to the present invention can be used in any electrostatographic printing system known in the art, electrophotography, ionography, direct electrostatic printing, etc. They are especially useful in classical electrophotography and in Direct Electrostatic Printing. When the toner particles in a composition according to this invention are magnetic they can also be used in magnetographic printing systems.
In toner compositions, used in the method according to present invention, the inorganic hydrophobic particles are simply mixed with the toner particles. It was found that, when the mixing proceeded in a way that also mechano-fusing of the particles in the toner surface appeared, (e.g. by long mixing times in an HENSCHEL mixer at temperatures higher than room temperature), the effect on gloss control was essentially the same as when the inorganic particles were simply mixed with the toner particles.
The toner particles, incorporated in a toner composition according to this invention, can comprise any toner resin known in the art and any known pigment or dye as long as said toner particles have a melt viscosity η such that 150 Pa.s (1,500 poise) ≤ η ≤ 2,000 Pa.s (20,000 poise). Preferably the toner particles have a melt viscosity η such that 250 Pa.s (2,000 poise) ≤ η ≤ 1,500 Pa.s (15,000 poise).
It was found that the limits on melt viscosity of the toner particles were quite critical. Too low melt viscosity (below 150 Pa.s) resulted in good fixing, but also in too high gloss that not could be diminished by the addition of different types of hydrophobic inorganic particles to the toner particles. Toner particles with too high melt viscosity (over 2,000 Pa.s) could not be properly fixed in a non-contact fusing process.
Thus the toner resin for toner particles useful in this invention is primarily chosen with emphasis on its melting behaviour, but also the other properties as chargeability, hardness, etc have to be considered.
The toner resin can be a polycondensation polymer or a mixture of polycondensation polymers as well as an addition polymer or a mixture of addition polymers. Also mixtures of polycondensation polymers and addition polymers are suitable as toner resin for toner particles according to the present invention. When polycondensation polymers are used, the use of polyesters is preferred.
Polyester resins suitable for use in toner particles according to the present invention are selected e.g. from the group of linear polycondensation products of (i) di-functional organic acids, e.g. maleic acid, fumaric acid, terephthalic acid and isophthalic acid and (ii) di-functional alcohols (diol) such as ethylene glycol, triethylene glycol, an aromatic dihydroxy compound, preferably a bisphenol such as 2,2-bis(4-hydroxyphenyl)propane called "Bisphenol A" or an alkoxylated bisphenol, e.g. propoxylated bisphenol examples of which are given in US-P 4,331,755. For the preparation of suitable polyester resins reference is made to GB-P 1,373,220.
When addition polymers are used, it is preferred to use styrene/acrylic resins. Preferred styrene-acrylic resins have a relatively high (more than 70 mol %) styrene content, and are more particularly copolymers of styrene-acrylic resins or styrene-methacrylic resins, e.g. copoly(styrene/n-butylmethacrylate) or copoly(styrene/2-ethyl-hexylacrylate).

Typical useful resins for the toner resin in toner particles according to the present invention are tabulated in table 1.

TABLE 1

N^o	Polymer	Tg °C	Meltvisco Pa.s
1	Polyester P1	50,5	140
2	Polyester P2	65	550
3	Polyester P3	63	700
4	Polyester P4	69	1600
5	Styr/acryl S1	67	1700
6	Styr/acryl S2	68	285
7	Styr/acryl S3	78	170
8	Styr/acryl S4	79	290
9	Styr/acryl S5	79.5	700
10	Styr/acryl S6	79	2250
Polyester P1 is ATLAC T500 (tradename). Polyester P2 is an aromatic polyester resin derived from terephthalic acid (100 mol %) as aromatic diacid and a mixture of DIANOL 33 (50 mol %) and ethylene glycol (50 mol %) as diols. Polyester P3 is an aromatic polyester resin derived from terephthalic acid (40 mol %), isophthalic acid (60 mol %) as aromatic di-acids and a mixture of DIANOL 22 (40 mol %) and ethylene glycol (60 mol %). DIANOL 22 is di-ethoxylated Bisphenol A. DIANOL 33 is di-propoxylated Bisphenol A. Bisphenol A = 4,4'isopropylidenediphenol. Polyester P4 is an aromatic polyester resin derived from terephthalic acid (64 mol %), isophthalic acid (36 mol %) as aromatic di-acids and ethylene glycol (100 mol %). Styr/acryl S1 is a copolymer of styrene and methyl acrylate in a 65/35 molar ratio. Styr/acryl S2 is a terpolymer of styrene, methyl acrylate and dimethylaminoethyl methacrylate in a 87/3/10 molar ratio. Styr/acryl S3, S4, S5 and S6 are a copolymer of styrene and methyl acrylate in a 80/20 molar ratio, only differing in molecular weight.

Preferred resins for use in toner particles have been disclosed in US 5,395,726, that is incorporated herein by reference. The resins disclosed in said patent and comprised in a toner composition according to the present invention are a mixture of resins, resin A and at least one resin B, characterized in that :

(1) said resin(s) A and said resin(s) B each have a glass transition temperature (Tg) larger than 45 °C,
(2) the Tg of said resin(s) A is at least 2.5 °C lower than the Tg of said resin(s) B,
(3) the melt viscosity (mvA) of said resin(s) A is at least 50 Pa.s and the melt viscosity (mvB) of said resin(s) B is within the scope of the following equation : $(mvB) = F x (mvA),$
wherein F is an integer from 2 to 20, and with a maximum value of (mvB) not exceeding 1,500 Pa.s, and
(4) the weight ratio of said resin(s) A and said resin(s) B in said powder particles is such that the deformability of the powder material is lower than 15 %, measured according to the method disclosed in US 5,395,726.

In an other preferred embodiment the toner particles comprise a resin mixture of at least two resins being selected in such a way that they have slight incompatibility with respect to each other. The HILDEBRAND parameter solubility for polymers is described in the book "Properties of Polymers" by D.W. Van Krevelen, 2nd. ed., Elseviers Scientific Publishing Company, New York, 1976, Chapter 7. The combination of the inorganic particles according to the present invention with toner particles comprising a resin mixture of at least two resins being selected in such a way that they have slight incompatibility with respect to each other, offers a useful method for gloss control.
In general the desired slight incompatibility can be obtained by combining a polyester resin P1 from table 1, e.g. a polyester, with an other polyester P2 from table 1, having a more polar character than said polyester resin P1. Such mixtures of resins and of resins and incompatible compounds have been disclosed in EP-A 656 129, which is incorporated herein by reference.
Especially when the abhesivity and the water repellency of the fixed layer of toner particles has to be enhanced, the toner resin of toner particles according to the present invention can comprise more than 3 % by weight with respect to the total resin content or can consist of a polysiloxane modified resin comprising polysiloxane moieties (PS) and other polymeric moieties (POL). Such resins are described in EP-A 740 217, that is included herein by reference.
For use in non-contact fusing systems it is often desired to diminish the energy needed to melt the toner and have a good fluidity at fairly low fixing temperature. Therefore it is preferred that toner particles, used in toner compositions according to the present invention, comprise as toner resin amorphous complex macromelecular compound that comprises in its macromelecular structure, (i) an amorphous polycondensation backbone, the corresponding backbone polymer having a Tg of at least 45 °C and (ii) at least one polymer chain being attached to said backbone, either terminally and/or in a side-chain, said polymer chain being derived from a polymer which on itself has an average molecular weight by number (M_avg) so that 400 ≤ M_avg ≤ 4,000, a melting point between 50 °C and 150 °C and a melting range of at most 15 °C. Such resins and toner particles comprising them are disclosed in EP-A 712 881, that is included herein by reference.
The toner particles, incorporated in a toner composition according to this invention, can be magnetic particles, incorporating a magnetic pigment, or can, preferably be non-magnetic. The non-magnetic toner particles in a toner composition according to this invention can beneficially be used in a two- (or multi) component developer, comprising a toner composition according to this invention together with magnetic carrier particles.
Toner particles, used in a toner composition according to the present invention, can have an average volume diameter between 1 and 50 µm, preferably between 3 and 20 µm. When the toner particles are intended for use in colour imaging, it is preferred that the volume average diameter is between 3 and 10 µm, most preferred between 3 and 8 µm. The particle size distribution of said toner particles can be of any type. It is however preferred to have an essentially (some negative or positive skewness can be tolerated, although a positive skewness, giving less smaller particles than an unskewed distribution, is preferred) Gaussian or normal particle size distribution, either by number or volume, with a coefficient of variability (standard deviation divided by the average) (ν) smaller than 0.5, more preferably of 0.3.
Toner particles, used in toner compositions according to the present invention, can comprise any normal toner ingredient e.g. charge control agents, pigments both coloured and black, anorganic fillers, etc. A description a charge control agents, pigments and other additives useful in toner particles, to be used in a toner composition according to the present invention, can be found in e.g. EP-A 601 235.
The images formed by deposition of a toner composition according to the present invention are preferably fixed in a non-contact fusing process. In such a process, there is no direct contact of the toner image with a solid heating body. Such non-contact fusing process includes a variety of embodiments, such as : (1) an oven heating process in which heat is applied to the toner image by hot air over a wide portion of the support sheet, (2) a radiant heating process in which heat is supplied by infrared and/or visible light absorbed in the toner, the light source being e.g. an infrared lamp or flash lamp, (3) a process wherein the heat is transferred to the toner layer by heating the side of the substrate opposite to the side carrying the image. This last process can be implemented in a non-contact system as well as by contacting said side opposite to the side carrying the image by heating means, e.g., a heated roller. In this invention the non-contact fusing systems described above under (1) and (2) are preferred. Thus this invention includes the use of toner compositions according to this invention in an electrostatographic method containing a non-contact fusing step, especially in those electrostatographic methods wherein said non-contact fusing step proceeds essentially by Infra Red (IR) radiation and optionally hot air. The invention thus includes also a method for electrostatographic imaging comprising the steps of :

i) providing a multi-component developer with magnetic carrier particles and a toner composition comprising toner particles and number n of different types of hydrophobic inorganic particles, said number n being at least 2, said toner particles containing a toner resin and having a melt viscosity η such that 150 Pa.s ≤ η ≤ 2,000 Pa.s, measured in a plate/plate rheometer at 120 °C and at 100 rotation/s and said toner particles further having an average BET surface (BET_ton) such that 0.4 m²/g ≤ BET_ton ≤ 1.5 m²/g, said n different types of inorganic particles each having an average BET surface (BET_ip1,...., BET_ipn) and each being present in said toner composition for A₁,...., A_n % by weight (% wt) with respect to the toner particles so that 150 ≤ BR ≤ 375 wherein $BR = \frac{i =1 n (A_{i} x ({BET}_{ip})_{i})}{{BET}_{ton}}$
ii) image-wise depositing said toner particles on a substrate, forming a toner image, and
iii) fixing said image to said substrate by non-contact fusing means.

In order to control the gloss in an image made by a toner composition according to the present invention and fixed in a non-contact fusing process, it may be beneficial to add post-treatment of the fixed image (i.e. the fused toner particles), with a pressure roller in order to further uniformize the image. The pressure roller exerts preferably a pressure on the fixed image of between 100 N/m and 500 N/m (where m expresses the linear nip-length), and the post-treatment proceeds for a time preferably between 30 and 150 msec.
Thus , the invention also encompasses a method for gloss control in electrostatically formed images comprising the steps of

i) using a toner composition according to this invention to deposit image wise toner particles on a substrate forming a toner image,
ii) fixing said toner image on said substrate by non-contact fusing and
iii) directly post-treating (without cooling) said fixed image with a pressure roller, said pressure roller having a temperature between 5 °C below Tg and 10 °C above Tg of said toner resin and said pressure roller applying a pressure between 100 N/m and 500 N/m (where m expresses the linear nip-length).

In a colour image, the amount and/or the dispersion of pigment in the toner particles, for a single colour, is adjusted such that a full saturated density in said colour is achieved by the deposition of a thin, almost single, layer of toner particles. By doing so the gloss differences, due to (great) differences in the height of the various layers of deposited toner particles, are minimized.
It is further preferred that, when using toner compositions according to the present invention, the amount of toner particles (Toner Mass, TM) being deposited to reach maximum optical density for each of the single colours follow the equation : $TM ≤0.8 × d_{v50} × ρ$
wherein TM is expressed in mg/cm², d_v50 is the average volume diameter of the toner particles expressed in cm, and ρ is the bulk density of the toner particles in mg/cm³. By maximum optical density for each of the single colours is meant an optical density on a reflecting support between 1.4 and 1.6 for yellow, magenta and cyan and an optical density between 1.6 and 2.0 for black.
Also when the image is finished by the application of a colourless toner as exemplified in, e.g., EP-A 656 129, EP-A 629 921, EP-A 486 235, US 5,234,783, US 4,828,950, EP-A 554 981, WO 93/07541 and Xerox Research Disclosure Journal, Vol.16, N^o 1, p. 69 (January/February 1991), it is beneficial to use a colourless toner composition according to the present invention. Also this colour less toner is deposited in an amount TM, fulfilling the equation above.
Thus, the invention also encompasses a toner composition, comprising toner particles and number n of different types of hydrophobic inorganic particles, characterised in that

i) said number n is at least 2,
ii) said toner particles comprise a toner resin and have a melt viscosity η such that 150 Pa.s ≤ η ≤ 2,000 Pa.s, measured in a plate/plate rheometer at 120 °C and at 100 rotation/s and an average BET surface (BET_ton) such that 0.4 m²/g ≤ BET_ton ≤ 1.5 m²/g,
iii) said n different types of inorganic particles have each an average BET surface (BET_ip1,...., BET_ipn) and are each present in said toner composition for A₁,...., A_n % by weight (% wt)) with respect to the toner particles so that 150 ≤ BR ≤ 375 wherein $BR = \frac{i =1 n (A_{i} x ({BET}_{ip})_{i})}{{BET}_{ton}}$
and
iv) said toner particles comprise an amount of colouring agent such that by depositing an amount TM of toner particles following the formula $TM ≤0.8 × d_{v50} × ρ$
wherein TM is expressed in mg/cm², d_v50 is the average volume diameter of the toner particles expressed in cm, and ρ is the bulk density of the toner particles in mg/cm³, yields maximum optical density.

EXAMPLES

1. Preparation of the toner particles

TONER 1 (T1)

49 parts of polyester P1 of Table 1 and 49 parts of polyester P3 of Table 1 were melt-blended for 30 minutes at 110 °C in a laboratory kneader with 2 parts of Cu-phthalocyanine pigment (Colour Index PB 15:3).
After cooling the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename). The average particle size of the separated toner was measured by Coulter Counter model Multisizer (tradename) and was found to be 8.0 µm by volume. This was a toner with BET_ton = 0.65 m²/g. The melt viscosity of the toner particles was 400 Pa.s as measured in a plate/plate rheometer (CARIMED RHEOMETER CSL 500 trade name of TA instruments Ltd, Dorking UK) at 120 °C and 100 rad/s.

TONER 2 (T2)

98 parts of polyester P1 of Table 1 were melt-blended for 30 minutes at 110 °C in a laboratory kneader with 2 parts of Cu-phthalocyanine pigment (Colour Index PB 15:3).
After cooling the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename). The average particle diameter of the separated toner was measured by Coulter Counter model Multisizer (tradename) was found to be 8.3 µm by volume. This is a toner having a BET surface BET_ton = 0.63 m²/g. The melt viscosity (η) of the toner particles was 150 Pa.s.

TONER 3 (T3)

98 parts of styrene/acrylate resin n° 10 (S6) of Table 1 were melt-blended for 30 minutes at 110 °C in a laboratory kneader with 2 parts of Cu-phthalocyanine pigment (Colour Index PB 15:3).
After cooling the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename). The average particle diameter of the separated toner was measured by Coulter Counter model Multisizer (tradename) was found to be 8.0 µm by volume. This is a toner having a BET surface BET_ton = 0.65 m²/g. The melt viscosity (η) of the toner particles was 2300 Pas.

2. The toner compositions

In table 2, the type of toner, the type inorganic particles, the BET surface of the inorganic particles and the amount of inorganic hydrophobic particles added to the toner particles to form toner compositions, described immediately hereafter are summarized.

TONER COMPOSITION 1 (TC1)

Toner 1 (T1), and one type inorganic hydrophobic particles were mixed using a HENSCHEL mixer with a filling factor of 30 % by volume, rotational speed 35 m/sec and during 30 sec.
The inorganic hydrophobic particles were hydrophobic fumed SiO₂ particles with specific surface area of 110 m²/g (AEROSIL R972).
The inorganic hydrophobic particles were added to the toner composition at a concentration of 1 parts for 100 parts of toner particles.

TONER COMPOSITION 2 (TC2)

The preparation of toner preparation TC1 was repeated, except that fumed hydrophobic SiO₂ with a specific surface area of 170 m²/g (AEROSIL R974) was mixed with the toner particles at a concentration of 1 part for 100 parts of toner particles.

TONER COMPOSITION 3 (TC3)

The preparation of toner composition TC1 was repeated, except that fumed hydrophobic SiO₂ with a specific area of 260 m²/g (AEROSIL R812) was added in a concentration of 1 part for 100 parts of toner particles.

TONER COMPOSITION 4 (TC4)

The preparation of toner composition TC1 was repeated except for concentration of the hydrophobic silica, which was now 0.5 parts for 100 parts of toner particles.

TONER COMPOSITION 5 (TC5)

The preparation of toner composition TC1 was repeated except that NO hydrophobic inorganic particles were present.

TONER COMPOSITION 6 (TC6)

The preparation of toner composition TC1 was repeated, except that hydrophobic precipitated SiO₂ with a specific area of 113 m²/g (SILICA SS20) was added in a concentration of 1 part for 100 parts of toner particles.

TONER COMPOSITION 7 (TC7)

The preparation of toner composition TC1 was repeated, except that hydrophobic precipitated SiO₂ with a specific area of 42 m²/g (SILICA SS70) was added in a concentration of 1 part for 100 parts of toner particles.

TONER COMPOSITION 8 (TC8)

The preparation of toner composition TC1 was repeated except that two types of inorganic hydrophobic particles were present. Hydrophobic fumed SiO₂ particles with specific surface area of 260 m²/g (AEROSIL R812) and hydrophobic precipitated SiO₂ particles with a specific surface area of 42 m²/g (SILICA SS70) were each added to the toner composition at a concentration of 0.5 part versus 100 parts of toner particles.

TONER COMPOSITION 9 (TC9)

The preparation of toner composition TC1 was repeated except that two types of inorganic hydrophobic particles were present. Hydrophobic fumed SiO₂ particles with specific surface area of 260 m²/g (AEROSIL R812) and hydrophobic precipitated SiO₂ particles with a specific surface area of 113 m²/g (SILICA SS20) were each added to the toner composition at a concentration of 0.5 part versus 100 parts of toner particles.

TONER COMPOSITION 10 (TC10)

The preparation of toner composition TC1 was repeated except that two types of inorganic hydrophobic particles were present. Hydrophobic fumed SiO₂ particles with specific surface area of 260 m²/g (AEROSIL R812) and hydrophobic TiO₂ particles with a specific surface area of 50 m²/g (TITANDIOXID T805) were each added to the toner composition at a concentration of 0.5 part versus 100 parts of toner particles.

TONER COMPOSITION 11 (TC11)

The preparation of toner composition TC10 was repeated except that each of the two types of hydrophobic inorganic particles was present for 0.3 parts for 100 parts of toner particles.

TONER COMPOSITION 12 (TC12)

The preparation of toner composition TC10 was repeated except that fumed hydrophobic silica (AEROSIL R812) was present for 0.5 parts for 100 parts of toner particles and hydrophobic TiO₂ (TITANDIOXID T805) for 0.7 parts for 100 parts of toner particles.

TONER COMPOSITION 13 (TC13)

The preparation of toner composition TC10 was repeated except that fumed hydrophobic silica (AEROSIL R812) was present for 0.45 parts for 100 parts of toner particles and hydrophobic TiO₂ (TITANDIOXID T805) for 0.65 parts for 100 parts of toner particles.

TONER COMPOSITION 14 (TC14)

The preparation of toner composition TC10 was repeated except that instead of fumed hydrophobic silica (AEROSIL R812), fumed hydrophobic silica with BET surface 170 m²/g (AEROSIL R974) was used.

TONER COMPOSITION 15 (TC15)

The preparation of toner composition TC14 was repeated except that instead of hydrophobic titania (TITANDIOXID T805), precipitated hydrophobic silica with BET surface 42 m²/g (SILICA SS70) was used.

TONER COMPOSITION 16 (TC16)

The preparation of toner composition TC10 was repeated except that toner T2 was used.

TONER COMPOSITION 17 (TC17)

3. The developer composition

With each of the toner compositions TC1 to TC17, a multi-component developer was prepared by mixing each composition to a coated ferrite carrier with a volume average particle size of 50 µm, at a concentration of 5% toner weight with resect to the carrier and activated for 30 minutes in order to attain a stable charge level.

4. The printing and evaluation of gloss

Images containing patches of even density were made on smooth copy paper at a deposition rate corresponding to a single, a double, a triple and a quadruple layer, corresponding to a full-colour system. In each layer 0.6 mg of toner particles /cm² were deposited. The images were fused by passing them through a contactless fusing station at 12.5 cm/sec over a length of 40 cm, applying heat to the substrate, such that the surface of the outcoming fused image had a temperature of 125°. The gloss was evaluated visually and given a quality figure, these figures are given in table 3. The figures have following meaning :

++: excellent evenness of the gloss
+: good evenness
0: acceptable evenness
-: uneven gloss
--: badly uneven gloss

In the same way the optical density (a measure of amount of transferred toner mass) was evaluated and ranked according to the following ranking figures :

++: excellent
+: good
0: acceptable
-: unacceptable
--: totally unacceptable

The results of the measurements are reported in table 3, together with the BET-ratio (BR), A₁ + A₂ and A₁/A₂.

TABLE 2

Ex #	Toner	Type**	IP₁* BET⁺	A₁ ⁺⁺	Type**	IP₂* BET⁺	A₂ ⁺⁺
TC1	T1	R972	110	1	-	-	-
TC2	T1	R974	170	1	-	-	-
TC3	T1	R812	260	1	-	-	-
TC4	T1	R812	260	0.5	-	-	-
TC5	T1	-	-	-	-	-	-
TC6	T1	SS20	113	1	-	-	-
TC7	T1	SS70	42	1	-	-	-
TC8	T1	R812	260	0.5	SS70	42	0.5
TC9	T1	R812	260	0.5	SS20	113	0.5
TC10	T1	R812	260	0.5	T805	45	0.5
TC11	T1	R812	260	0.3	T805	45	0.3
TC12	T1	R812	260	0.5	T805	45	0.7
TC13	T1	R812	260	0.45	T805	45	0.65
TC14	T1	R974	170	0.5	T805	45	0.5
TC15	T1	R974	170	0.5	SS70	42	0.5
TC16	T2	R812	260	0.5	T805	260	0.5
TC17	T3	R812	260	0.5	T805	260	0.5

* Hydrophobic particles of type 1 and type 2 respectively
** Rxxx are fumed hydrophobic silica particles and Txxx are fumed hydrophobic titania (TiO₂) particles, sold under tradename AEROSIL Rxxx or TITANDIOXID Txxx, by Degussa AG, Germany. SSxx are hydrophobic silica particles sold by NIPPON SILICA of Japan, under tradename SILICA SSxx.
⁺ in m²/g
⁺⁺ in % by weight with respect to toner particles.

It is clear from table 3 that when no inorganic particles or only one type of inorganic particles is present (TC1 to TC7) gloss can be controlled when the BET-ratio is within the scope of formula I, with n = 1, however the optical density is in the best of the examples only acceptable. When two types of inorganic particles are present and the melt viscosity of the toner particles is 400 Pa.s (TC8 to TC15) both gloss control and optical density are good, and it is seen that it is possible when hydrophobic silica and hydrophobic titania are present (e.g., TC10, TC12 and TC13), both gloss control and optical density are excellent. When the melt viscosity of the toner resin is either 150 or 2,300, the gloss control is no longer possible (see TC16 and TC 17 in comparison to TC10).

Claims

A toner composition comprising toner particles and number n of different types of hydrophobic inorganic particles, characterised in that
i) said number n is at least 2,

ii) said toner particles comprise a toner resin and have a melt viscosity η such that 150 Pa.s ≤ η ≤ 2,000 Pa.s, measured in a plate/plate rheometer at 120 °C and at 100 rotation/s and an average BET surface (BET_ton) such that 0.4 m²/g ≤ BET_ton ≤ 1.5 m²/g and

iii) said n different types of inorganic particles have each an average BET surface (BET_ip1,...., BET_ipn) and are each present in said toner composition for A₁,...., A_n % by weight (% wt)) with respect to the toner particles so that 150 ≤ BR ≤ 375 wherein $BR = \frac{i =1 n (A_{i} x ({BET}_{ip})_{i})}{{BET}_{ton}}$
A toner composition according to claim 1, wherein 200 ≤ BR ≤ 330.
A toner composition according to claim 1 or 2, wherein n = 2.
A toner composition according to claim 3, comprising a first type of inorganic hydrophobic particles (IP1) having a BET specific surface (BET_ip1) > 200 m²/g and a second type of inorganic particles (IP2) having a BET specific surface (BET_ip2) so that 30 m²/g < BET_ip2 ≤ 100 m²/g.
A toner composition according to claim 3 or 4, wherein said first type of inorganic particles is present in an amount of A₁ % by weight (% wt) with respect to said toner particles and said second type of inorganic particles is present in an amount of A₂ % by weight (% wt) with respect to said toner particles so that 0.25 % wt < A₁ + A₂ < 2.5 % wt and 0.4 < A₁/A₂ < 2.
A toner composition according to claim 5, wherein said inorganic particles IP1 are hydrophobic SiO₂ particles and said inorganic particles IP2 are hydrophobic TiO₂ particles.
A toner composition according to any of the preceding claims, wherein said toner particles comprise an amount of colouring agent such that by depositing an amount TM of toner particles following the formula $TM ≤0.8 × d_{v50} × ρ$
wherein TM is expressed in mg/cm², d_v50 is the average volume diameter of the toner particles expressed in cm, and ρ is the bulk density of the toner particles in mg/cm³, yields maximum optical density.
A toner composition according to any of the preceding claims, wherein said toner particles are non-magnetic.
Use of a toner composition according to claim 8 in a multi-component developer, together with magnetic carrier particles.
Use of a toner composition according to any of claims 1 to 8, in an electro(stato)graphic printing method wherein the image is fused by non-contact fusing means.
A method for gloss control in electrostatically formed images comprising the steps of :
i) using a toner composition according to any one of claims 1 to 8, to deposit image wise toner particles on a substrate forming a toner image,

ii) fixing said toner image on said substrate by non-contact fusing and

iii) directly post-treating (without cooling) said fixed image with a pressure roller, said pressure roller having a temperature between 5 °C below Tg and 10 °C above Tg of said toner resin and said pressure roller applying a pressure between 100 N/m and 500 N/m (where m expresses the linear nip-length).
A method for gloss control in electrostatically formed images according to claim 11, wherein after said step of non-contact fusing said image is allowed to cool and said pressure roller having a temperature of between 10 °C below and 10 °C above the softening temperature of said toner resin and said pressure roller applying a pressure between 100 N/m and 500 N/m (where m expresses the linear nip-length).