EP0813118A2

EP0813118A2 - Toner for two-component type developer

Info

Publication number: EP0813118A2
Application number: EP97303745A
Authority: EP
Inventors: Yoshitake Shimizu; Kazuya Nagao; Masatomi Funato; Seijiro Ishimaru; Masatoshi Toshimitsu
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1996-06-10
Filing date: 1997-06-03
Publication date: 1997-12-17
Also published as: CN1172277A; KR980003894A; TW340198B; EP0813118A3

Abstract

There is provided a toner for a two-component type developer, which comprises (i) toner particles comprising a fixing resin having anionic polar groups, a coloring agent, and a magnetic powder which is used in an amount of 0.1 to 5 parts by weight for 100 parts by weight of the fixing resin, and (ii) an additive comprising silica, alumina and titania, and being adhered on surfaces of the toner particles in a total amount of 0.15 to 2 parts by weight for 100 parts by weight of the toner particles, and contains substantially no charge control agent. The toner exhibits a stable chargeability during a long-term use without generation of a spent toner. As a result, the toner suppresses the image fogging and the toner scattering, and ensures a stable image density and a high image quality for a long term.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a toner for a two-component type developer and, more particularly, to a toner for a two-component type developer which contains no charge control agent, and is suitably used in a so-called electrophotographic image forming apparatus such as an electrostatic copying machine or a laser beam printer.
In an electrophotographic image forming apparatus, the surface of its photoconductor is first exposed to light, whereby an electrostatic latent image is formed thereon. Then, the surface of the photoconductor is brought into contact with a developer by a developing unit. Thus, a toner contained in the developer adheres onto the electrostatic latent image, which is developed into a toner image. The toner image is transferred from the photoconductor surface onto a paper surface and fixed thereon, whereby an image corresponding to the electrostatic latent image is formed on the paper surface.
Generally used as the developer is a two-component type developer containing a toner and a carrier essentially comprising magnetic particles such as iron particles and ferrite particles. The carrier serves to apply a charge to the toner by way of triboelectrification and, at the same time, to supply the toner to an electrostatic latent image with the toner adsorbed on the surface of the carrier.
The toner for use in the two-component type developer typically contains a fixing resin, a coloring agent (e.g., carbon black), a release agent (e.g., wax) and a charge control agent. The charge control agent is used to control the amount of triboelectric charge of the toner which influences the image development and transfer. The choice of the charge control agent is the most important for a toner design. Exemplary charge control agents include an electron donative substance and an electron attractive substance, which respectively allow the toner to be positively and negatively charged.
Where such a conventional toner is used, however, a toner component (particularly, the charge control agent) is liable to adhere onto the surface of the carrier over long-term use so that so-called "spent toner" is generated.
Therefore, the carrier has a surface charge state similar to that of the toner particles. Particularly, where the toner has a small particle diameter, each toner particle has a small charge so that even a small amount of the spent toner causes a charging failure. This results in a shorter lifetime of the developer, reduced chargeability, image fogging, image transfer failure and toner scattering.
Furthermore, many of commonly used charge control agents contain a heavy metal, like a chromium-containing dye, thereby presenting a safety problem.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a toner for a two-component type developer, which comprises: toner particles comprising a fixing resin having anionic polar groups, a coloring agent, and a magnetic powder which is used in an amount of 0.1 to 5 parts by weight for 100 parts by weight of the fixing resin; and an additive comprising silica, alumina and titania, and being adhered on surfaces of the toner particles in a total amount of 0.15 to 2 parts by weight for 100 parts by weight of the toner particles; wherein a methanol extract of the toner exhibits an absorbance of substantially zero in the wavelength range of 400 nm to 700 nm and has no absorption peak in the wavelength range of 280 nm to 350 nm.
The toner of the present invention can have any or all of the following advantages:

(1) The toner is free from the generation of a spent toner even over long-term use and ensures the formation of a high-quality image of a sufficient density at a high transfer efficiency.
(2) The toner includes no charge control agent containing a heavy metal such as chromium, (3) exhibits a stable chargeability for a long time to suppress image fogging and toner scattering, and (4) ensures the formation of a high-quality image density over a long time.
(5) The methanol extract of the toner exhibits an absorbance of substantially zero in the wavelength range of 400 nm to 700 nm, and has no absorption peak in the wavelength range of 280 nm to 350 nm, as described above. Absorption peaks in these wavelength ranges are attributable to a charge control agent. This means that the toner of the present invention contains substantially no charge control agent. Therefore, the present invention prevents an abrupt charge reduction which may otherwise be caused due to migration and adhesion of the charge control agent onto the carrier surface as in the prior art toner.
(6) The fixing resin in the toner of the present invention has anionic polar groups. Therefore, the reduction in the chargeability can be prevented which may otherwise be caused due to the absence of the charge control agent.
(7) Since the magnetic powder is dispersed in the fixing resin, the toner in a magnetic brush is held on the carrier by a magnetic attraction force as well as a coulomb force at the image development. This prevents the toner contamination inside a copying machine and the formation of a foggy copy image due to the toner scattering. Particularly in a case that the toner has a small particle diameter and each toner particle has a smaller charge, this effect is advantageous, so that the developing sensitivity is improved and the formation of a fog-free and high-density image is ensured.
(8) The magnetic powder is contained in a proportion of 0.1 to 5 parts by weight per 100 parts by weight of the fixing resin. Therefore, the chargeability of the toner is stabilized. This increases the image density and remarkably suppresses the toner scattering.
(9) The additive is blended in a predetermined amount for the surface modification of the toner particles. Silica, alumina and titania function as a fluidity improving agent, as a charging rate improving agent and as a surface resistance modifier, respectively. Since a toner having a small particle diameter is liable to lead to an insufficient image density and image fogging, the addition of titania is particularly useful for reducing the resistance of the toner while maintaining a sufficient chargeability. Thus, a sufficient image density can be maintained and the image fogging can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a graphical representation illustrating the absorbance of a methanol extract of a toner obtained in Example 1; and
Fig. 2 is a graphical representation illustrating the absorbance of a methanol extract of a toner obtained in Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The toner particles according to the present invention may be prepared by blending the magnetic powder, a coloring agent such as pigment, a release agent and the like in the fixing resin.
The fixing resin to be used in the present invention has anionic polar groups. The fixing resin may be obtained by polymerizing a monomer having an anionic polar group or by copolymerizing such a monomer with other monomer. The fixing resin is preferably a block copolymer, a random copolymer or a graft copolymer of a monomer having an anionic polar group and other monomer(s).
Examples of monomers having an anionic polar group include those having a carboxyl group, a sulfo group (-SO₃H), a phosphono group (-PO(OH)₂) and the like, among which monomers having a carboyxl group are preferred.
Examples of specific monomers having a carboxyl group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid and fumaric acid, monomers that can form a carboxyl group such as of maleic anhydride, and monoalkyl esters of dicarboxylic acids such as maleic acid and fumaric acid. Examples of specific monomers having a sulfo group include styrene sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid. Examples of specific monomers having a phosphono group include 2-phosphonopropyl methacrylate, 2-phosphonoethyl methacrylate and 3-chloro-2-phosphonopropyl methacrylate.
The monomer having an anionic polar group may be a free acid; a salt of an alkaline metal such as sodium, potassium, a salt of an alkaline earth metal such as calcium or magnesium, or a salt of zinc or the like.
The other monomer(s) to be polymerized with the monomer having an anionic polar group as required are selected so that the resulting polymer can have a sufficient fixability and chargeability required of the toner. Vinyl monomers may be used as the second monomer either alone or in combination. Examples of vinyl monomer include acrylate monomers, aromatic monovinyl monomers, vinyl ester monomers, vinyl ether monomers, diolefin monomers and monoolefin monomers.
Examples of specific acrylate monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, β-hydroxyethyl acrylate, γ-hydroxypropyl acrylate, δ-hydroxybutyl acrylate and β-hydroxyethyl methacrylate.
Examples of specific aromatic monovinyl monomers include styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, o-, m- or p-chlorostyrene and p-ethylstyrene.
Examples of specific vinyl ester monomers include vinyl formate and vinyl propionate.
Examples of specific vinyl ether monomers include vinyl methyl ether, vinyl ethyl ether, vinyl n-butyl ether, vinyl phenyl ether and vinyl cyclohexyl ether.
Examples of specific diolefin monomers include butadiene, isoprene and chloroprene.
Examples of specific monoolefin monomers include ethylene, propylene, isobutylene, 1-butene, 1-pentene and 4-methyl-1-pentene.
Examples of the resin having anionic polar group, i.e., a polymer or copolymer obtained through the polymerization or copolymerization of any of the aforesaid monomers, include styrene-acrylic acid copolymers, styrene-maleic acid copolymers and ionomer resins. Also usable is a polyester resin having anionic polar group.
Where the anionic polar group is present in the form of a free acid in the fixing resin, the fixing resin preferably contains the anionic polar group in such a proportion that the acid value thereof is within a range of 2 to 30, more preferably 5 to 15. In the case that some or all of the anionic polar groups are neutralized, the anionic polar group may be present in the fixing resin in a such proportion that, if the anionic polar groups are assumed to be present in the form of a free acid, the acid value would be within the same range as described above. If the acid value of the resin, i.e., the concentration of the anionic polar groups, is lower than the aforesaid range, the chargeability of the resulting toner tends to be insufficient. If the acid value exceeds the aforesaid range, the resulting toner may have an undesirable hygroscopic property.
In the present invention, the resin having anionic polar groups may be blended with another resin having no anionic polar group for use as the fixing resin. In such a case, the proportion of the anionic polar groups in the entire fixing resin is preferably the same as described above.
Exemplary materials for the magnetic powder include magnetite (Fe₃O₄), ferrites, maghemite (γ-Fe₂O₃), CrO₂, and powdery iron alloys.
Examples of specific ferrites include zinc iron oxide (ZnFe₂O₄), yttrium iron oxide (Y₃Fe₅O₁₂), cadmium iron oxide (CdFe₂O₄), gadolinium iron oxide (Gd₃Fe₅O₁₂), copper iron oxide (CUFe₂O₄), lead iron oxide (PbFe₁₂O₁₂), nickel iron oxide (NiFe₂O₄), neodymium iron oxide (NdFeO₃), barium iron oxide (BaFe₁₂O₁₉), magnesium iron oxide (MgFe₂O₄), manganese iron oxide (MnFe₂O₄), and lanthanum iron oxide (LaFeO₃). These ferrites are used in a particulate form either alone or in combination. Preferably used is magnetite in a fine particulate form, more preferably in a regular octahedral fine particulate form. The magnetic powder preferably has an average particle diameter of 0.05 to 5 µm, more preferably 0.05 to 1 µm.
The magnetic powder may have a high electrical resistance or a low electrical resistance, but typically has a volume resistivity of 1 x 10^-1 to 1 x 10⁹ Ω·cm, preferably 1 x 10¹ to 1 x 10⁶ Ω·cm.
A toner containing such magnetic powder is well known as a magnetic toner, which is used for a one-component type developer containing no carrier. The magnetic toner contains the magnetic powder in a high proportion, typically in a proportion of 20 to 80 parts by weight unlike the toner of the present invention.
In the present invention, the magnetic powder is blended in a proportion of 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, more preferably 0.5 to 3 parts by weight for 100 parts by weight of the fixing resin. If the content of the magnetic powder exceeds 5 parts by weight, the electrical resistance of the resulting developer is undesirably increased thereby to reduce the image density. If the content is less than 0.1 part by weight, the resulting toner cannot enjoy a stabilization effect which would be expected from the addition of the magnetic powder.
Examples of specific coloring agents to be blended in the fixing resin include carbon black, lamp black, aniline black, acetylene black, Chrome Yellow, Hansa Yellow, Benzidine Yellow, Betulin Yellow, Quinoline Yellow, Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Watchung Red, Permanent Red, Brilliant Carmine 3B, Brilliant Carmine 6B, Du Pont Oil Red, Pyrazolone Red, Lithol Red, Rhodamine B Lake, Lake Red C, Rose Bengal, Aniline Blue, Ultramarine Blue, Chalcoil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Phthalocyanine Green, Malachite Green, oil-soluble dyes (such as C. I. Solvent Yellow 60, C. I. Solvent Red 27, and C. I. Solvent Blue 35), etc. These coloring agents may be used either alone or as a mixture.
The coloring agent is preferably blended in a proportion of 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, most preferably 5 to 15 parts by weight per 100 parts by weight of the fixing resin.
Examples of the release agent (offset preventive agent) include aliphatic hydrocarbons, metal salts of fatty acids, higher fatty acids, fatty acid esters and saponified substances thereof, silicone oil and various waxes. Among those, aliphatic hydrocarbons having an average molecular weight of about 1,000 to about 10,000 are particularly preferred. Examples of specific release agents include lower molecular weight polypropylene, lower molecular weight polyethylene, paraffin wax, lower molecular weight olefine polymers including a polymer unit of an olefin having four or more carbons, and silicone oil. These may be used either alone or in combination.
The release agent may be blended in a proportion of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight for 100 parts by weight of the fixing resin.
The toner particles of the present invention can be prepared by a dry method including mixing, pulverizing and sieving steps or by a wet method including the step of spray-powdering a toner dispersion. The resulting toner particles are classified by way of air classification for obtaining toner particles in a desired particle diameter range.
In the present invention, the diameters of the toner particles are not particularly limited, but may be in an ordinary diameter range. Where the toner particles are used for a small diameter toner, the volume-based average particle diameter thereof (median diameter as measured by means of a Coulter counter) is preferably 5 to 11 µm, more preferably 7 to 10 µm to ensure the formation of a high-quality image.
The additive to be added as the surface treatment agent for surface modification of the toner particles contains silica (silicon dioxide), alumina (aluminium oxide) and titania (titanium (IV) oxide), as described above.
The silica preferably has an average particle diameter of 5 to 100 nm, more preferably 7 to 50 nm. The alumina preferably has an average diameter of 5 to 1,000 nm, more preferably 7 to 500 nm. The titania preferably has an average diameter of 5 to 1,000 nm, more preferably 7 to 200 nm.
The silica, the alumina and the titania are preferably each added in a proportion of 0.05 to 1 part by weight, more preferably 0.05 to 0.8 parts by weight for 100 parts by weight of the toner particles, provided that the total amount thereof is 0.15 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight per 100 parts by weight of the toner particles.
If the total amount of the additive is less than 0.15 parts, a surface modification effect on the toner particles cannot be expected. Conversely, if the total amount exceeds 2 parts by weight, a portion of the additive not adsorbed onto the toner particles is left in a free state to adhere (or film) on the photoconductor.
If the proportion of the silica is less than 0.05 parts by weight, the silica tends not to function as a fluidity improving agent. Conversely, if the proportion exceeds 1 part by weight, the chargeability may be undesirably increased, resulting in a reduced image density.
If the proportion of the alumina is less than 0.05 parts by weight, the alumina may not function as a charging rate improving agent. Since alumina is substantially non-polar, the alumina adhering onto the surfaces of the toner particles allows the toner particles to be quickly charged up to a saturation charge level with the absolute value of the saturation charge kept constant. As a result, the chargeability can be stabilized throughout the lifetime of the developer. If the proportion of the alumina exceeds 1 part by weight, the chargeability may be reduced because alumina is substantially non-polar but slightly positively charged.
If the proportion of the titania is less than 0.05 parts by weight, it may not be possible to reduce the resistance of the resulting toner, resulting in a reduced image density. Conversely, if the proportion exceeds 1 part by weight, the resistance may be extremely reduced, thereby aggravating image fogging.
In the present invention, a higher fatty acid metal salt is preferably blended in addition to the aforesaid additive to prevent the additive and the toner particles from adhering onto the photoconductor. The higher fatty acid metal salt functions as a lubricant and prevents the adhesion (or filming) of the additive and the toner particles onto the photoconductor.
Exemplary higher fatty acid metal salts include metal salts of higher fatty acids having ten or more carbons. Examples of specific higher fatty acids include saturated fatty acids such as undecylic acid, lauric acid, myristic acid, palmitic acid and stearic acid, among which stearic acid is particularly preferred. Examples of specific metals to form the metal salt include zinc, magnesium, aluminum, calcium, chromium, mercury, cerium, iron, sodium, potassium, lead and barium. Among those, zinc stearate and magnesium stearate are preferred. These higher fatty acid metal salts may be used either alone or in combination.
The higher fatty acid metal salt may be blended in a proportion of 0.001 to 0.5 parts by weight, preferably 0.003 to 0.3 parts by weight per 100 parts by weight of the toner particles. The additive and the higher fatty acid metal salt may be mixed in predetermined amounts with the toner particles so as to be allowed to adhere onto the surfaces of the toner particles. A Henschel mixer or a ball mill, for example, may be used for the mixing. The additive and the higher fatty acid metal salt may be added simultaneously or separately.
The carrier to be used in combination with the toner of the present invention is not particularly limited, but any of conventionally used carriers may be used. For example, a magnetic carrier such as a sintered ferrite of copper-zinc-magnesium ferrite is preferably used. The magnetic carrier may be used as it is, but preferably coated with a silicone resin, a fluorine resin, an epoxy resin, an amino resin or a urethane resin. The carrier preferably has particle diameters of 30 to 200 µm, more preferably 50 to 150 µm, and a saturation magnetic force of 30 to 70 emu/g, more preferably 45 to 65 emu/g
The mixing ratio of the carrier and the toner is typically 98:2 to 90:10, preferably 97:3 to 94:6.
As described above, the toner for the two-component type developer according to the present invention, though containing no charge control agent, can have stable toner characteristics and prevent the reduction in the image density and the transfer efficiency which may otherwise be caused due to insufficient charging. Since the toner of the present invention contains no charge control agent, the production costs can be reduced and the lifetimes of the toner and the carrier can be extended.
Where the toner has smaller particle diameters, i.e., a volume-based average particle diameter of 5 to 11 µm, the formation of high-quality images may be achieved over a long time. In addition, toner scattering, image fogging and deterioration of the transfer efficiency can be effectively prevented.

EXAMPLES

The toner for a two-component type developer according to the present invention will hereinafter be described in detail by way of Examples and Comparative Examples. It should be noted that the toner of the present invention be not limited to these examples.

Example 1

A styrene-acryl copolymer having carboxyl groups (prepared by copolymerizing styrene, butyl methacrylate and acrylic acid in a weight ratio of 70:28:2) was used as the fixing resin. Carbon black and magnetite (a magnetic material available from Titan Industry Co., Ltd. under the trade name of "BL-100" and having an average particle diameter of 0.5 µm) were mixed with the fixing resin in the following mixing ratio, and the resulting mixture was melt-kneaded by means of a biaxial extruder. Then, the resulting product was pulverized by means of a jet mill, and classified by means of an air-classification machine to give toner particles having an average particle diameter of 8.0 µm.

(Composition of toner particles) (Parts by weight)

Fixer resin 100

Carbon black 10

Magnetite 2

The following additives were added to the toner particles, and mixed for 2 minutes by means of a Henschel mixer to give a toner. It is noted that the following proportions are expressed on the basis of parts by weight with respect to 100 parts by weight of the toner particles.

(Additives)	(Parts by weight)
Hydrophobic fine silica particles (Average particle diameter: 0.02 µm)	0.3
Fine alumina particles (Average particle diameter: 0.02 µm)	0.3
Fine titania particles (Average particle diameter: 0.05 µm)	0.3

Fig. 1 shows the absorbance curve of a methanol extract of the resulting toner in the wavelength range of 200 to 800 nm. As shown, the methanol extract had substantially no peak in the wavelength range of 280 to 350 nm, and exhibits an absorbance of substantially zero in the wavelength range of 400 nm to 700 nm. This means that the methanol extract did not have any peak attributable to a charge control agent.

Example 2

A toner was prepared in substantially the same manner as in Example 1 except that, after the additives were added to and mixed with the toner particles, zinc stearate was added to the resulting mixture and mixed for two minutes by means of a Henschel mixer.
Fig. 2 shows the absorbance curve of a methanol extract of the resulting toner in the wavelength range of 200 to 800 nm. As shown in Fig. 2, the methanol extract had substantially no peak in the wavelength range of 280 to 350 nm, and exhibits an absorbance of substantially zero in the wavelength range of 400 nm to 700 nm. This means that the methanol extract did not have any peak attributable to a charge control agent, like Example 1.

Comparative Examples 1 to 9

Toners were prepared in substantially the same manner as in Example 1, except that the respective toners had compositions as shown in Tables 1 to 3.

Evaluation Tests

A ferrite carrier having an average particle diameter of 70 µm was blended with the toners respectively prepared in Examples and Comparative Examples, and homogeneously mixed for preparation of two-component type developers each having a toner concentration of 3.5%. With the use of the respective developers, 100,000 copies were made by means of an electrophotographic copying machine (available from Mita Industrial Co., Ltd. under the trade name of "DC-7085"), and then the developers were each evaluated in the following manner.
Used as an original document for the copying was a character document including black character portions in an area ratio of 8%. After the 100,000 copies were made, a copy was sampled by using an original document including black portions with a solid black portion in an area ratio of 15%.
The methods for the evaluation tests were as follows:

(a) Measurement of Image Density

The density of a solid black portion of each of the copy images sampled at the start and after the formation of the 100,000 copies was measured by means of a reflection densitometer (available from Tokyo Denshoku Co., Ltd., Model TC-6D).

(b) Measurement of Fog Density

The density of a non-image portion of each of the copy images sampled at the start and after the formation of the 100,000 copies were measured by means of a reflection densitometer (available from Tokyo Denshoku Co., Ltd., Model TC-6D).

(c) Measurement of Charged Amount

The charged amount of 200 mg of the developer was measured at the start and after the formation of the 100,000 copies by a blow-off powder charge measuring device (available from Toshiba Chemical Co., Ltd.), and an average charge per gram of the toner was calculated.

(d) Resolution

Copies were made with the use of a predetermined chart original (bearing a plurality of patterns each including a predetermine number of parallel lines per millimeter) at the start and after the formation of the 100,000 copies, and the obtained copy images were visually observed for evaluation of resolution.

(e) Transfer Efficiency

The amounts of the toner in the toner hopper were measured before the formation of a copy (O copy) and after the formation of 100,000 copies. A consumed toner amount after the formation of the 100,000 copies was calculated from a difference between the toner amounts before the formation of a copy and after the formation of the 100,000 copies.
Meanwhile, the amount of the toner collected through a cleaning process during the formation of the 100,000 copies was measured. The toner transfer efficiency was calculated on the basis of the toner consumption (A) and the collected toner amount (B) from the following equation: $Transfer Efficiency (%) = (A - B)/A$

(f) Amount of Spent Toner

After the formation of the 100,000 copies, the developer was sampled. The sample was placed on a 400-mesh sieve, and then sucked through the sieve by a blower for separation of the toner and the carrier. Thereafter, 5 g of the carrier left on the sieve was weighed and put in a beaker, and toluene was added thereto to dissolve a toner component adhering onto the surface of the carrier. The toluene solution was discarded with the carrier attracted onto the bottom of the beaker by means of a magnet. This operation was repeated until the resulting toluene solution became transparent. Then, the resulting carrier was heated in an oven to evaporate toluene adhering thereto, and the resulting residue was weighed. A difference between the weight of the carrier put in the beaker and the weight of the residue obtained after the evaporation of toluene was determined as the amount of a spent toner. The amount of the spent toner was expressed as the weight (mg) of the toner component adhering onto 1g of the carrier.

(g) Filming

After the formation of the 100,000 copies, the surface of the photoconductor was visually observed for judging the occurrence of filming on the photoconductor on the following criteria:

++:: No filming
+:: Substantially no filming
-:: Slight filming
--:: Notable filming

(h) Toner Scattering

After 100,000 copies were made, the toner scattering state in the copying machine was visually observed and evaluated on the following criteria:

+:: No toner scattered
-:: Toner slightly scattered
--:: Toner scattered

(i) Fluidity

The toner was charged in a container, and allowed to fall from an opening formed at the bottom of the container. At this time, the amount of the toner falling within a predetermined time period was measured and expressed as a fluidity index for evaluation of the fluidity of the toner. The container used for the measurement had an opening having a length of 100 mm and a width of 0.1 mm formed at a taper angle of 60° at the bottom thereof. The container further had a brass roller disposed above the opening and having a diameter of 16 mm and an undulated surface. The toner fall amount was determined on the basis of the amount of the toner falling within 5 minutes with the roller rotated at a rotation speed of 3 rpm.

The evaluation results are shown in Tables 1 to 3.

Table 1

	Unit	Example 1	Example 2	Comparative Example 1
Toner composition
Average diameter of toner	µm	8.0	8.0	8.0
Carboxylic acid in resin	-	Yes	Yes	No
Magnetic powder Content	pbw*	2	2	2
Charge control agent	-	No	No	No
Silica content	pbw*	0.3	0.3	0.3
Alumina content	pbw*	0.3	0.3	0.3
Titania content	pbw*	0.3	0.3	0.3
Higher fatty acid metal salt	-	No	Yes	No

Copying characteristics and properties
Image density
1st sample	-	1.49	1.48	1.50
2nd sample	-	1.47	1.46	1.51
Fog density
1st sample	-	0.002	0.002	0.003
2nd sample	-	0.004	0.002	0.012
Charge
1st sample	-µC/g	24	24	18
2nd sample	-µC/g	21	22	15
Resolution
1st sample	Lines/mm	6.3	6.3	5.0
2nd sample	Lines/mm	6.3	6.3	5.0
Transfer efficiency
1st sample	wt%	80	82	70
2nd sample	wt%	75	77	52
Spent toner amount	mg	0.137	0.125	0.195
Filming	-	+	++	+
Toner scattering	-	+	+	-
Fluidity	g/5 min	5.6	5.5	5.0
1st sample: A copy obtained at the start. 2nd sample: A copy obtained after the formation of the 100,000 copies. * pbw: parts by weight

Table 2

	Unit	Comparative Examples
		2	3	4	5
Toner composition
Average diameter of toner	µm	8.0	8.0	8.0	8.0
Carboxylic acid in resin	-	Yes	Yes	Yes	Yes
Magnetic powder Content	pbw*	2	0	6	2
Charge control agent	-	Cr-complex	No	No	No
Silica content	pbw*	0.3	0.3	0.3	0.3
Alumina content	pbw*	0.3	0.3	0.3	0.3
Titania content	pbw*	0.3	0.3	0.3	0.0
Higher fatty acid metal salt	-	No	No	No	No

Copying characteristics and properties
Image density
1st sample	-	1.49	1.44	1.28	1.35
2nd sample	-	1.48	1.28	1.09	1.37
Fog density
1st sample	-	0.002	0.001	0.001	0.003
2nd sample	-	0.020	0.010	0.003	0.004
Charge
1st sample	-µC/g	24	28	22	28
2nd sample	-µC/g	20	18	24	25
Resolution
1st sample	Lines/mm	6.3	5.6	6.3	5.6
2nd sample	Lines/mm	5.6	5.6	4.5	5.6
Transfer efficiency
1st sample	wt%	78	77	70	78
2nd sample	wt%	60	63	62	70
Spent toner amount	mg	0.158	0.201	0.215	0.189
Filming	-	+	+	+	+
Toner scattering	-	-	--	+	+
Fluidity	g/5 min	5.2	4.8	4.9	5.5
1st sample: A copy obtained at the start. 2nd sample: A copy obtained after the formation of the 100,000 copies. *pbw: parts by weight

Table 3

	Unit	Comparative Examples
		6	7	8	9
Toner composition
Average diameter of toner	µm	8.0	8.0	8.0	8.0
Carboxylic acid in resin	-	Yes	Yes	Yes	Yes
Magnetic powder Content	pbw*	2	2	2	2
Charge control agent	-	No	No	No	No
Silica content	pbw*	0.3	0.0	0.03	0.8
Alumina content	pbw*	0.0	0.3	0.03	0.8
Titania content	pbw*	0.3	0.3	0.03	0.8
Higher fatty acid metal salt	-	No	No	No	No

Copying characteristics and properties
Image density
1st sample	-	1.47	1.52	1.40	1.51
2nd sample	-	1.51	1.49	1.33	1.47
Fog density
1st sample	-	0.002	0.002	0.003	0.002
2nd sample	-	0.008	0.006	0.009	0.007
Charge
1st sample	-µC/g	26	18	19	25
2nd sample	-µC/g	17	18	16	23
Resolution
1st sample	Lines/mm	5.6	5.6	5.6	6.3
2nd sample	Lines/mm	5.6	5.6	5.6	4.5
Transfer efficiency
1st sample	wt%	80	79	65	83
2nd sample	wt%	68	69	52	80
Spent toner amount	mg	0.201	0.179	0.235	0.129
Filming	-	+	+	+	--
Toner scattering	-	-	-	--	+
Fluidity	g/5 min	5.1	2.5	3.1	6.2
1st sample: A copy obtained at the start. 2nd sample: A copy obtained after the formation of the 100,000 copies. *pbw: parts by weight

As can be understood from Tables 1 to 3, the toners which include no charge control agent, a fixing resin having anionic polar groups, toner particles containing a predetermined amount of magnetic powder, toner particles containing a silica, an alumina, and a titania as an additive, and a predetermined total amount of silica, alumina and titania can maintain a chargeability sufficient for the development during a prolonged use, thereby preventing the charging failure. Thus, the toners ensure the formation of a high density image, while preventing the image fogging, the generation of spent toner, the filming and the toner scattering.

Claims

A toner for a two-component type developer, which comprises:
toner particles comprising a fixing resin having anionic polar groups, a coloring agent, and a magnetic powder which is used in an amount of 0.1 to 5 parts by weight for 100 parts by weight of the fixing resin; and

an additive comprising silica, alumina and titania, and being adhered on surfaces of the toner particles in a total amount of 0.15 to 2 parts by weight for 100 parts by weight of the toner particles;

wherein a methanol extract of the toner exhibits an absorbance of substantially zero in the wavelength range of 400 nm to 700 nm and has no absorption peak in the wavelength range of 280 nm to 350 nm.
A toner according to claim 1, wherein the silica, the alumina and the titania are each present in an amount of 0.05 to 1 part by weight with respect to the toner particles.
A toner according to claim 1 or 2, wherein a higher fatty acid metal salt is adhered on the surfaces of the toner particles.
A toner according to any preceding claim, wherein the toner particles have a volume-based average particle diameter of 5 to 11 µm.
A toner according to claim 4, wherein the toner particles have a volume-based average particle diameter of 7 to 10 µm.
A toner according to any preceding claim, wherein the fixing resin is a polymer or a copolymer resulting from polymerization or copolymerization using a monomer having an anionic polar group.
A toner according to claim 6, wherein the anionic polar group is a carboxyl group, a sulfo group or a phosphono group.
A toner according to any preceding claim, wherein the coloring agent is present in an amount of 1 to 30 parts by weight for 100 parts by weight of the fixing resin.
A toner according to any preceding claim, wherein the magnetic powder is magnetite.
A toner according to any previous claim, wherein the magnetic powder is present in an amount of 0.1 to 5 parts by weight for 100 parts by weight of the fixing resin.