GB2151034A - Toner for developing latent electrostatic images - Google Patents

Abstract

A toner for developing latent electrostatic images comprises (1) toner particles comprising a binder resin and a colouring agent or magnetic material: and (2) from 0.1 to 20 parts by weight per 100 parts by weight of the toner particles of spacer particles formed of silicon carbide, silicon nitride, boron carbide, zirconium oxide or chrome oxide and having a particle size of from 0.1 to 20 mu m.

Description

SPECIFICATION Toner for developing latent electrostatic images The present invention relates to a toner for developing latent electrostatic images as formed, for example, in electrophotography, electrostatic printing and electrostatic recording.

Generally, latent electrostatic images are developed by means of a toner comprising as main component fine particles comprising a binder resin, a colouring agent or magnetic material and, optionally, a polarity control agent. After development, the developed toner images are fixed to a support material. A variety of fixing methods are known, such as the direct-contact image fixing method using, for example, heating rollers which come directly into contact with the toner images and fix the toner images to the support material; and the non-contact image fixing method using, for example, heating plates by which the toner images are indirectly heated and fixed to the support material.The direct-contact image fixing method using heating rollers is particularly advantageous in image-fixing performance compared with the non-contact image fixing method using heating plates because the former method has better heat transfer efficiency than the latter.

When toner images are fixed to a support material by the direct-contact image fixing method using heating rollers, it is necessary that the binder resin contained in the toner be sufficiently softened for image fixing at the heating temperature of the heating rollers. Furthermore, the toner should have good release properties so that it releases from the surface of the heating rollers and does not adhere thereto.

Some conventional toners in fact meet the above requirements. However, they have the shortcoming that the toner images become excessively glossy after image fixing and the image density thereof becomes too high, so that image quality is significantly degraded. This occurs particularly when the surface of the image fixing rollers is coated with a fluorine-containing resin. Possibly this occurs because the toner images formed on a support material are caused to pass through the heating rollers for fixing, the toner images are fused and depressed simultaneously, so that the surface of the toner images becomes overly smooth and glossy.

It is an object of the present invention to provide a toner for developing latent electrostatic images, capable of providing fixed toner images having high image quality which are not excessively glossy and the image density of which is not too high.

A toner according to the invention comprises (1) toner particles comprising a binder, a colouring agent or magnetic material, and, optionally, a polarity control agent, together with (2) hard, fine spacer particles having a Mohs' hardness of 8 or more in order to reduce the pressure applied to toner images, for instance by heating rollers. Specifically, the hard, fine spacer particles are formed of silicon carbide, silicon nitride, boron carbide, zirconium oxide or chrome oxide and have a particle size of from 0.1 ,um to 20 ym. The spacer particles are employed in an amount of from 0. 1 to 20 parts by weight per 100 parts by weight of the toner particles.

A toner according to the invention can be prepared by conventional methods. Specifically, a mixture of a binder agent and a colouring agent or a magnetic material is melted and kneaded.

The mixture is then cooled to room temperture, crushed and classified, so that conventional toner particles are obtained. If desired, a polarity control agent can be added to the abovementioned mixture. Then there are added to 100 parts by weight of the thus prepared toner particles, from 0. 1 to 20 parts by weight of hard, fine spacer particles form of silicon carbide, silicon nitride, boron carbide, zircinium oxide or chrome oxide and having a particle size of from 0.1 to 20 lim.

The spacer particles should have a particle size of from 0.1 to 20 lim. If the particle size is less than 0.1 ym, the particles do not serve as spacers between the toner particles and the heating rollers since they are smaller than the particle size of the toner particles and, as a result, the toner particles are depressed by the heating rollers and the toner images become glossy after image fixing. In contrast. if the particle size of the spacer particles is more than 20 ym, the toner particles cannot be fixed properly, so that non-fixed portions, so-called "halos", may be formed in the toner image areas.

The spacer particles should be present in an amount of from 0.1 to 20 parts by weight per 100 parts by weight of the toner particles. If the amount of spacer particles is less than 0.1 part by weight, they do not serve effectively as spacers, so that the toner images become glossy after image fixing. In contrast, if the spacer particle content is more than 20 parts by weight, the toner particles cannot be properly fixed to the support material.

The spacer particles for use in the present invention should have a Mohs' hardness of 8 or more.

Silicon oxide, titanium oxide and aluminium oxide, which are conventionally employed materials in toners, however, cannot be used in the present invention due to the following shortcomings.

Silicon oxide and titanium oxide are hard materials and therefore can be used for preventing toner images from becoming glossy. However, since they have a high charging polarity, when they are added in a large amount to toner particles in order to prevent the formation of glossy toner images, the quantity of electric charge of the toner particles decreases or occasionally the polarity of the toner particles may be reversed. The reversing of the polarity of the toner particles is apt to occur particularly when the charging polarity of the toner is positive. The result is that the toner deposits on the background when these oxides are used. Therefore, these oxides cannot be used in practice in the present invention.

When aluminium oxide is employed in the present invention, the overall electric resistivity of the toner decreases to a large extent due to the low electric resistivity of aluminium oxide. As a result the toner cannot hold sufficient charge for development of latent electrostatic images and toner deposition on the background also takes place. For this reason, aluminium oxide cannot be employed in the present invention, either.

In the present invention, when a non-magnetic toner is prepared, it is preferable that the toner particles contain from 60 to 90 wt.% of binder, from 5 to 40 wt.% of colouring agent and from 0.5 wt.% to 5 wt.% of polarity control agent. When a magnetic toner is prepared, it is preferable that the toner particles containing from 40 to 80 wt.% of binder, from 20 to 60 wt.% of magnetic material and from 0.5 to 5 wt.% of polarity control agent.

Binders which may be used in the present invention include the following resins, namely: styrene polymers and substituted styrene polymers such as polystyrene, poly-p-chlorostyrene and polyvinyltoluene; styrene type copolymers such as styre- / styrene/chlorostyrene copolymers: styre- ne/propylene copolymers, styrene/vinyltoluene copolymers; styrene/vinylnaphthalene copolymers, styrene/methyl acrylate copolymers; styrene/ethyl acrylate copolymers; styrene/butyl acrylate copolymers; styrene/octyl acrylate copolymers; styrene/methyl methacrylate copolymers, styrene/ethyl methacrylate copolymers; styrene/butyl methacrylate copolymers; styrene/methyl a-chlorn-methacrylate copolymers; styrene/acrylonitrile copolymers; styrene /vinyl methyl ether copolymers; styrene/vinyl ethyl ether copolymers; styrene/vinyl methyl ketone copolymers; styrene/butadient copolymers; styrene/ isoprene copolymers: styrene/acrylonitrile indene copolymers; styrene/maleic acid copolymers; maleic acid ester copolymers; polymethylmethacrylate; polybutyl methacrylate; polyvinyl chloride; polyvinyl acetate; polyethylene; polypropylene; polyesters; polyurethanes; polyamides; epoxy resins; polyvinyl butyrals; polyacrylic acid resins; rosin; modified rosins; terpene resins; phenolic resins; aliphatic or alicyclic hydrocarbon resins; aromatic petroleum resins; chlorinated paraffins; and paraffin waxes. The binders can be used along or in combination.

Suitable colouring agents for use in the present invention include, for example, the following conventional colouring agents namely: carbon black, nitrosine dye, Aniline Blue, Calconyl Blue, Chrome Yellow, Ultramarine Blue, Du Pont Oil Red, Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue, Malachite Green Oxalate, Lamp Black, Oil Black, Azo Oil Black, Rose Bengale and mixtures of two or more of the above colouring agents.

As magnetic materials for use in the present invention, these are preferably employed materials which are chemically stable and in the form of fine particles having a particle size of 1 ,um or less, for example, magnetite (tri-iron tetroxide). Representative examples of other such magnetic or magnetizable materials are metals such as cobalt, iron and nickel, alloys and mixtures of aluminum, cobalt, copper, iron. lead, magnesium, nickel, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten and vanadium; metal compounds containing metal oxides such as aluminium oxide, iron oxide copper oxide, nickel oxide, zinc oxide, titanium oxide and magnesium oxide; refractory nitrides such as vanadium nitride and chromium nitride; carbides such as tungsten cvarbide and silicon carbide; ferrite; and mixtures of the above-mentioned materials.

As polarity control agents that can be added to the toner particles, conventional polarity control agents can be used, such as quaternary ammonium salts, organic dyes, in particular base dyes and salts thereof. Specific examples of such polarity control agents are stearyldimethylbenzylammonium chloride, benzyldimethylhexadecylammonium chloride, decyltrimethyl ammonium chloride, Nigrosine base, nigrosine hydrochloride, Safranine y and Crystal Violet.

In order that the invention may be well understood, the following examples are given by way of illustration only. In the examples all parts and percentages are by weight unless otherwise stated.

Example 1 Parts Styrene-n-butyl acrylate copolymer (70:30) 80 Carbon Black 1 5 Nigrosine base EX 5 The above compounds were mixed and dispersed in a mixer. The mixture was then kneaded by means of heated rollers. After the kneaded mixture had cooled, it was ground and classified, to give toner particles having a particle size of from 5 to 1 5 ,um. To the thus prepared toner particles, 3 parts of silicon carbide having a particle size of 2 ym and a Mohs' hardness of 1 3 were added as spacer particles and the mixture was dispersed by a speed kneader, whereby a toner according to the invention was prepared.

Comparative Example 1 The procedure of Example 1 was repeated except that the silicon carbide employed as spacer particles in Example 1 were not added.

Example 2 Parts Styrene-n-butyl methacrylate copolymer (70:30) 90 Carbon black 8 Nigrosine base EX 2 The above components were mixed and dispersed in a mixer. The mixer was then kneaded by means of heated rollers. After the kneaded mixture had cooled, it was ground and classified, to give toner particles having a particle size of from 5 to 1 5 ym. To the thus prepared toner particles, 3 parts of chrome oxide having a particle size of 3 ym and a Mohs' hardness of 9 are added as spacer particles and the mixture was dispersed by a speed kneader to give a toner according to the invention.

Comparative Example 2 The procedure of Example 2 was repeated except that the chrome oxide employed as spacer particles in Example 2 was not added.

Example 3 Parts Styrene-n-butyl acrylate copolymer (70:30) 85 Carbon black 10 Stearyldimethylbenzylammonium chloride 5 The above components were mixed and dispersed in a mixer. The mixture was then kneaded by means of heated rollers. After the kneaded mixture was cooled, it was ground and classified, to give toner particles having a particle size of from 5 to 1 2 ym. To the thus prepared toner particles, 5 parts of zirconium oxide having a particle size of 0.5 ym and a Mohs' hardness of 11 were added as spacer particles and the mixture was dispersed by a speed kneeder to give a toner according to the invention.

Comparative Example 3 The procedure of Example 3 was repeated except that the chrome oxide employed as spacer particles in Example 3 was not added.

Example 4 Parts Styrene-n-butyl acrylate copolymer (70:30) 45 Tri-iron tetroxide 50 Nigrosine base EX 5 The above components were mixed and dispersed in a mixer. The mixture was then kneaded by means of heated rollers. After the kneaded mixture had cooled, it was ground and classified to give toner particles having a particle size of from 5 to 1 2 ym. To the thus prepared toner particles, 5 parts of silicon carbide having a particle size of 5 lim and a Mohs' hardness of 1 3 were added as spacer particles and the mixture was dispersed by a speed kneader to give a toner according to the invention.

Comparative Example 4 The procedure of Example 4 was repeated except that the silicon carbide employed as spacer particles in Example 4 was not added.

The thus prepared toners were subjected to image fixing tests by forming a latent electrostatic image on a photoconductor corresponding to a solid image having a diameter of 30 mm by a conventional electrophotographic process, developing the latent electrostatic image with each toner, transferring the developed toner image with a deposition of 1.0 + 0.2 mg/cm2 of the toner to an image transfer sheet and fixing the toner image to an image transfer sheet by an image fixing apparatus including heating rollers coated with a fluorine-containing resin for a commerically available copying machine (Ricopy FT 4700 made by Ricoh Company, Ltd.).The results were as follows: Toner of Image Densitiy Form of Comparative Image Example Example Density No. 1 1.31 No. 1 1.58 No. 2 1.35 No. 2 1.60 No. 3 1.30 No. 3 1.50 No. 4 1.28 No. 4 1.55 As can be seen from the above results, the toner images obtained with the toners according to the present invention had appropriate image densities as compared with the excessively high image densities obtained with the comparative toners.

Furthermore, the toner images obtained with the toners according to the present invention were not glossy despite the use of the heating rollers coated with a fluorine-containing resin. In contrast to this, the toner images obtained by the comparative toners were glossy, poor in image quality and inappropriate for practical use.

With respect to the fixing of the toner images to the image transfer sheet, the toners according to the present invention and the comparative toners were both excellent.

Claims (9)

1. A toner for developing latent electrostatic images comprising 1) toner particles comprising a binder resin and a colouring agent or magnetic material; and (2) from 0.1 to 20 parts by weight per 100 parts by weight of the toner particles of spacer particles formed of silicon carbide, silicon nitride, boron carbide, zirconum oxide or chrome oxide and having a particle size of from 0.1 to 20 ym.

2. A toner as claimed in claim 1, in which the binder is polystyrene, poly-p-chlorostyrene, polyvinyl toluene, a styrene/p-chlorostyrene copolymer, a styrene/propylene copolymer, a styrene/vinyltoluene copolymer, a styrene/vinylnaphthalene copolymer, a styrene/methyl acrylate copolymer, a styrene/ethyl acrylate copolymer, a styrene/butyl acrylate copolymer, a styrene/octyl acrylate copolymer, a styrene/methyl methacrylate copolymer. a styrene/ethyl methacrylate copolymer, a styrene/butyl methacrylate copolymer, a styrene/methyl sv-chlorome- thacrylate copolymer, a styrene/acrylonitrile copolymer, a styrene/vinyl methyl ether copolymer, a styrene/vinyl ethyl ether copolymer, a styrene/vinyl methyl ketone copolymer, a styrene/butadiene copolymer, a styrene/isoprene copolymer, a styrene/acrylonitrile/indene copolymer, a styrene/maleic acid copolymer, a styrene/maleic acid ester copolymer, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, a polyester, a polyurethane, a polyamide, an epoxy resin, a polyvinyl butyral, a polyacrylic acid resin, rosin, a modified rosin, a terpene resin, a phenol resin, an aliphatic hydrocarbon resin, an alicyclic hydrocarbon resin, an aromatic petroleum resin, a chlorinated paraffin or a paraffin wax.

3. A toner as claimed in claim 1 or claim 2, in which the toner particles further comprise from 0.5 to 5% by weight of a polarity control agent.

4. A toner as claimed in claim 3 in which the polarity control agent is stearylqlimethylbenzy- lammonium chloride, benzyldimethylhexadecylammonium chloride, decyltrimethyl ammonium chloride, Nigrosine base, nigrosine hydrochloride, Safranine y or Crystal Violet.

5. A toner as claimed in claim 3 or claim 4 in which the toner particles comprise from 60 to 90% by weight of the binder resin and from 5 to 40% by weight of the colouring agent.

6. A toner as claimed in any one of the proceding claims in which the said colouring agent is carbon black, nigrosine dye, Aniline Blue, Calconyl Blue, Chrome Yellow, Ultramarine Blue, Du Pont Oil Red, Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue, Malachite Green Oxalate, Lamp Black, Oil Black, Azo Oil Black or Rose Bengale.

7. A toner as claimed in claim 2 or claim 3 in which the toner particles comprise from 40 to 80 wt.% of the binder resin and from 20 to 60 wt/% of the magnetic material.

8. A toner as claimed in any one of claims 1 to 4 and 7 in which the magnetic material is cobalt, iron or nickel; an alloy or mixtures of aluminium, cobalt, copper, iron, lead, magnesium, nickel, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten or vanadium; a metal compound containing aluminium oxide, iron oxide, copper oxide, nickel oxide, zinc oxide, titanium oxide or magnesium oxide; a refractory nitride; a carbide; or ferrite.

9. A toner as claimed in claim 1 substantially as hereinbefore described with reference to the examples.