GB2222269A - Electrophotographic toner - Google Patents

Description

1 -W Y 1 1 n 1.

2 2 2. 22 6% 9 ELECTROPEOTOGRAPHIC TONER BACKGROUND OF THE INVENTION

The present invention relates to an electrophotographic toner for developing an electrostatic latent image.

In electrophotography, two types of developers are commonly used to render the electrostatic latent image on a light-sensitive layer visible: one-component developers made of toners prepared by melt-blending resins such as polystyrene, styrene-butadiene copolymers and polyesters with colorants selected f rom among pigments and dyes such as carbon black and phthalocyanine blue, and then f inely dividing the mixture; and twocomponent developers having toners mixed with carriers that are in the form of glass beads or metal (e.g., iron, nickel and ferrite) particles, optionally coated with various resins, which have sizes substantially equal to the toner size or up to 500 pm.

These developers, however, have had the problem that when they are used alone, desired characteristics with respect to the quantity of electric charge, the charging speed, charge exchangeability, uniform charging, the dependency of image quality on the environment and developer's durability. In an attempt at alleviating these disadvantages, charge control agents have often been incorporated in developers.

one of the methods employed on the basis of this idea is to incorporate silica in developers of a type that is to be negatively charged, but the resulting developers do not have high developing ability or satisfactory charge exchange in toners, and there is a high likelihood that toners of opposite polarity will form to increase the chance of fogging. It is also known to use silica in toners of a type that is to be positively charged but in this case, too, fogging will easily occur on account of the formation of toners of opposite polarity. Unexamined Published Jar)anese Patent Application No. 62-129866 proposes using not only fine silica particles but also titania par-ticles not larger than 0.05 lim as an external additive. However, even this technique can not completely prevent fogging.

SUMMAREY OF THE INVENTION An. object, therefore, of the present invention is to provide a toner that hardly generates fogging that would otherwise be caused by the formation of toners of opposite polarity.

DETAILED DESCRIPTION OF THE INVENTION

The electrophotographic toner of the present invention comprises at least a colorant and a binder resin 2 - 4 and is characterized in that both a fine silica powder having an average particle size of no greate r than 0.05 pm and titania particles having an average particle size of at least 0.1 pm are deposited on the surfaces of toner particles.

The f ine silica powder to be used in the present invention is not limited to any particular type as long as it has an average particle size not exceeding 0.1 pm. A preferred example is a fine silica powder hydrophobic by treatment with a known agent dimethyldichlorosilane. Specific examples of silica powder that can be used, include R972 rendered such as the fine and R812 available from Nippon Aerosil Co., Ltd. The fine silica powder is used in amounts ranging from 0.1 to 3.0 wt%, preferably from 0. 2 to 1.5 wt%.

Any ititania particles having an average particle size of at least 0.1 pm may be used in the present invention but those having an average size in the range oft 0.1-1.0.pm. are preferred. Specific examples of the titania particles that may be used in the present invention include KA-10 and KR460 available from Titan Kogyo Kabushiki Kaisha. The titania particles are used in amounts ranging from 0.1 to 3.0 wt%, preferably from 0.2 to 2. 0 wt%.

The toner particles on the surfaces of which the fine silica powdei and titania particles described above are to be deposited, are not limited to any particular type and any toner particles that are composed of known colorants and known binder resins may be employed.

Binder resins that can be used in toner particles include homopolymers and copolymers of styrenes such as styrene, chlorostyrene, and vinylstyrene; monoolefins such as ethylene, propylene, butylene, and. isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, and vinyl benzoate; a-methylene aliphatic monocarboxylic acid esters V such as methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl butyl ether; and vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropenyl ketone. Typically used binder resins inc-lude- polystyrene, a styrene- acrylic acid alkyl ester copolymer, a styrene-methacrylic acid alkyl ester copolymer, a styrene-acrylonitrile copolymer, a styrenebutadiene copolymer, a styrene-maleic anhydride copolymer, polyethylene and polypropylene. In addition, polyesters, polyurethanes, epoxy resins, silicone resins, polyamides, modified rosins, paraffins and waxes can be used.

Y 1 Typical examples of the colorants that can be used in the toner include: carbon black, nigrosine dyes, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DU Pont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengale, C.I. pigment red 48:1, C.I. pigment red 122, C.I. pigment red 57:1, C.I. pigment yellow 97, C.I. pigment yellow 12, C.I. pigment blue 15:1, C.I. pigment blue 15:3, etc.

If desired, the toner particles may contain other additives such as known charge control agents and fixing aids.

The toner particles used in the present invention have an average particle size that is preferably not greater than about 30 pm, more preferably in the range of 3-20 pm.

The electrophotographic toner of the present invention may be of a onecomponent type which does not use a carrier or of a twocomponent type which uses a carrier. Preferably, the toner of the present invention is used as a two-component developer.

if carriers are to be used, known carriers may be used without any particular limitation as exemplified by iron powder carriers, ferrite carriers, surface-co.at ferrite carriers, and magnetic powder dispersion type carriers.

In preparing the elect rophotographi c toner of the present invention, the fine silica powder and titania particles described above may be deposited on the surfaces of toner particles by known means, such as a Henschel mixer or a blender with a V-shaped vessel which are employed for mixing purposes.

The present invention will be described in greater detail with reference to the following examples.

Example 1

Styrene-n-butyl methacrylate 90 wt% crosslinked copolymer Carbon black 10 wt% The above-listed components were melt-kneaded, and k-hen pulverized and classified to obtain toner particles having an average particle size of 11 Um. Thereafter, 0.8 wt% of a fine silica powder (average particle size, 0.016 Um; a-vailable from Nippon Aerosoil Co., Ltd. under the trade name R972) and 1.0 wt% of titania particles (average particle size, 0.4 pm; available from Titan Kogyo Kabushiki Kaisha under the trade name KA-10) were added to the toner particles, and the respective components were mixed in a Henschel mixer to have the silica and titania particles deposited on the surfaces of the toner particles.

In the next step, 30 wt% of a styrene-n-butyl methacrylate copolymer and 70 wt% of magnetite (EPT 1000 of Toda Industrial Co., Ltd.) were kneaded, comminuted and classified to make a carrier powder having an average particle size of 35 pm.

The previously prepared toner (7 wt%) was mixed with 93 wt% of the carrier to prepare an electrophotographic developer. When this developer was subjected to a copying test with an elect rophotographic machine (adapted from FX-7790 by Fuji Xerox Co., Ltd.), up to 5 x 105 copies could be taken without experiencing fogging due to wrong sign toner.

Com,Darative Example 1 A toner and a carrier were prepared and processed into an electrophotographic developer as in Example 1 except that titania particles were not used. When a copying test was conducted on the developer as in Example 1, up to 2 x 105 copies could be taken with satisfactory results but no more copies could be obtained without experiencing fogging due to wrong sign toner.

Comparative Example 2 A toner and a carrier were prepared and processed into an electrophotographic developer as in Example 1 except that the titania particles were replaced by 1.0 wt% of far smaller titania particles (average particle size, 0.021 pm; available from Nippon Aerosil Co., Ltd. under the trade name P25). When a copying test was conducted on the developer as in Example 1, up to 3 x 105 copies could be taken with satisfactory results but no more copies could be obtained without experiencing fogging due to wrong sign toner.

Example 2

Styrene-n-butyl methacrylate 90 wt% crosslinked copolymer Copper phthalocyanine 9 Wt% Charge control agent (Bon.'%--ron.P-51.of Orient Chemical Industry Co., Ltd.) 1 Wt% The above-lis'#.-ed components were melt-kneaded, pulverized and classified to make toner particles having an average particle size of 11 pm. To the resulting toner particles, 0.3 wt% of a fine silica powder (average particle size, 0.007 pm; available from Nippon Aeroxil Co., Ltd. under the trade name R812) and 1.0 wt% of titania particles (average particle size, 0.3 pm; available from Titan Kogyo Kabushiki Kaisha under the trade name KR-460) were added and the respecti.ve components were mixed in a Henschel mixer to have the t j! 1 - tJ silica and titania particles deposited on the surfaces of the toner particles.

In the next step, a carrier was made as in Example 1 and 93 wt% of this carrier was mixed with 7 wt% of the toner to prepare a developer. When this developer was subjected to a copying test with an electrophotographic machine (adapted from FX-7790 by Fuji Xerox Co., Ltd. ), up to 5 x 105 copies could be taken without experiencing fogging due to wrong sign toner.

Example 3

A toner was prepared as in Example 2 except that 9 wt96 of copper phthalocyanine was replaced by 9 wt% of C.I. pigment red 48:1.. This toner was mixed with a carrier and processed to form an electrophotographic developer as in Example 2. When a copying test was conducted on the resulting developer as in Example 2, up to 5 x 105 copies could be taken without experiencing fogging due to toners of opposite polarity.

As described on the foregoing pages, the electrophotographic toner of the present invention is characterized in that a fine silica powder with an average particle size of no greater than 0.1 lim and titania particles with an average particle size of at least 0.1 um are deposited on the surfaces of toner particles. Because of this constitution, even if the toner is repeatedly used for a long term, wrong sign toner are hardly produced so that copies with stable image quality having no fogging can be obtained.

Claims (4)

CLAIMS:

1. An electrophotographic toner comprising at least-a colorant and a binder resin, wherein a fine silica powder having an average particle size of no greater than 0.05 pm and titania particles having an average particle size of at least 0.1 pm are deposited on the surfaces of toner particles.

2. An electrophotographic toner according to claim 1, wherein said fine silica powder is made of hydrophobic silica.

3. An electrophotographic toner according to claim 2, wherein said fine silica powder is included in said toner in amounts of 0.1 to 3.0 wt% and said titania particles are included in amounts of 0.1 to 3.0 wt%.

4. An electrophotographic toner according to claim 3, wherein said toner particles have an average particle size of about 30 pm or less.

Published 1990 at The Patent Offic,'. State House. 66 171 Hip Holborn, London WClR4TP. Further coplesmaybe obtainedfrOm The Patent Office Sales Branch. St Mary Cray. Orpingtor,. Kel-t BR5 LIRD. Pvrted by Wil.lipiex techniques Ita. St Mary Cray, Kent. Con. 1187