GB2114310A - Electrostatic image toner - Google Patents

Abstract

A toner for the development of an electrostatic image consists essentially of particles having an average particle diameter upon particle size volume distribution within a range of 6 to 10 mu m and a particle diameter of the greatest number of particles upon particle size number distribution within a range of 5 to 8 mu m, the number of particles having a particle diameter of less than 5 mu m being not more than 15 % of whole particle number and the number of particles having a particle diameter of more than 16 mu m being not more than 2 % of whole particle number. A developer for electrostatic image consists essentially of particles of the toner and a carrier having an average particle size within the range 50-120 mu m.

Description

SPECIFICATION Electrostatic image developer and toner therefor Brief Summary of the Invention: This invention relates to a developer for developing electrostatic images produced according to such methods as an electrophotographic method, an electrostatic recording method, an electrostatic printing method and the like as well as a toner adapted to be applied thereto.

Brief Description of the Drawing: Figure 1 is a schematic plain view for illustrating shape of one embodiment of carriers for the present developer.

Detailed Description of the Invention: Presently there have been widely utilized such processes for forming a visible image through an electrostatic image, but development with a developer should be requisite for making visible the electrostatic image. There have been hitherto proposed a variety of types of electrostatic image developers and, of these developers, the so-called two component-system developer is preferably capable of forming a rather sharp visible image as compared with other types of developers.This two component-system developer is composed of a toner and a carrier, a toner is charged to a special polarity by triboelectric of the toner with the carrier through agitation and the toner is made adhered onto a support of electrostatic image by the use of electrostatic attraction force between said triboelectric charge and electrostatic charge forming the electrostatic image to accomplish the desired development.

The toner in such a two component-system developer comprises binder resin particle having dispersed therein a coloring agent such as carbon black and the like. Generally, the smaller a particle diameter thereof is, the higher sharpness in visible image becomes and the toner practically used is composed of a particle group having an average particle diameter upon particle size volume distribution of 10-15,um and a considerably broad range of particle diameter distribution.

The toner particle diameter or its distribution could remarkably affect a quality of the so formed visible image and there have been disclosed such technique in Japanese Patent Laid Open Applications No. 134636/1979 and No. 72054/1979.

However, such prior art toner has a rather higher ratio of the number of fine particles with a particle diameter of less than 5 'lem. Accordingly, smooth supply of toner is difficult because of its low fluidity and triboelectric charge-to-mass ratio (hereinafter Q/M) in toner is changed or varied to produce change in density, gray background and so on in the formed visible image, together with insufficient cleaning of photoreceptor and toner scattering to contaminate the interior of a copying machine, which leads to loss of effect on sharpness of visible image. As discussed hereinabove, if a toner particle dimaeter is reduced for increasing sharpness of visible image, the desired superior visible image could not have been formed actually on various grounds.

This invention has been completed upon the aforesaid circumstances as a result of our earnest studies.

It is accordingly a primary object of this invention to provide a developer for electrostatic image which can form visible image with a high quality, namely superior sharpness and gradation.

Another object of this invention is to provide an electrostatic image developer having a good fluidity of a toner with less toner scatter.

Another object of this invention is to provide an electrostatic image developer having a larger ratio of carbon black in a toner, a higher blackness of a toner and a better triboelectric charge characteristics of a toner by a carrier and capable of accomplishing favourable development.

Other objects of this invention is to provide a developer for electrostatic image which has a broad allowable range for a toner concentration and an excellent durability and also provides a stable triboelectric charge state in a toner.

Still another object of this invention is to provide a toner for the above-mentioned developer which shows superior fixing and offset-preventing properties, broad temperature range for fixation, good shelf life and charge property and excellent developability as well as formation of a high quality visible image with sharpness and gradation.

These and other objects and advantages of this invention will be apparent from the following description.

According to one aspect of this invention, there is provided a developer for electrostatic image which comprises a toner particle and a carrier, said particle having an average particle diameter upon particle size volume distribution within a range of 6 to 10 ELm and a particle diameter of the greatest number of particles upon particle size number distribution within a range of 5 to 8 'lem, the number of particles having a particle diameter of less than 5 m being not more than 15 % of whole particle number and the number of particles having a particle diameter of more than 16 ELm being not more then 2 % of whole particle number.

According to another aspect of this invention, there is also provided a toner for the development of an electrostatic image which consists essentially of particles having an average particle diameter upon particle size volume distribution within a range of 6 to 10,um and a particle diameter of the greatest number of particles upon particle size number distribution within a range of 5 to 8 ill, the number of toner particles having a particle diameter of less than 5 ym being not more than 1 5 % of whole particle number and the number of toner particles having a particles diameter of more than 16 clam being not more than 2 % of whole particles number.

In this specification, particle size distribution of the toner or carrier is measured by means of Coulter Counter Model "TA II" (manufactured by Coulter Electric Co., Ltd., U.S.A.) with an aperture tube having a diameter of 100 elm for the toner or with the tube having a diameter of 500 m for the carrier.

More particularly, the present developer comprises the two component system of the specific toner and carrier and can produce various advantageous results, as obviously seen from the under-mentioned examples, typically, a high sharp visible image without any gray background by accurate development of even fine image portions, a great increase or improvement in stability of development and so on.

Then, the toner and carrier in the present developer will be more particularly described hereinbelow.

Toner In the present toner, the specific ratios of fine particle and large particle provide a sufficient fluidity to the toner with less toner scattering and satisfactory cleaning of a photoreceptor and without any production of the so-called "dust". If the average particle diameter on particle size volume distribution is more than 10 ELm or the diameter of said greatest number of particle is more than 8 m, a high sharpness can not be attained. Also, if the former diameter is less than 6 ,um or the latter diameter is less than 5 pm (including the case where a ratio of fine particle is more than 1 5 %), there could not be eliminated the prior art defects upon larger ratio of fine particle.

In the present toner, one embodiment is a toner composed of a binder resin containing as a main component a styrene component and having dispersed therein 10-30 % by weight of acidic carbon black. In this embodiment, said binder resin is a copolymer containing the underdefined A % by weight of a styrene and a resin forming said carrier coating layer is a copolymer containing the under-defined B % by weight of a styrene, the ratio of said A/B satisfying the formula "0.7 < A/B < 3.0".

As another binder resin which may be employed in the present toner, there is provided the binder resin which comprises as a main component resin a copolymer of at least 3 monomer components, wherein one of said 3 monomer components is a styrene monomer component and other two components are selected from an alkyl acrylate monomer and an alkyl methacrylate monomer and preferably the one is an alkyl acrylate monomer component and the other is an alkyl methacrylate monomer component.

As examples of the styrene monomer which may give the styrene monomer component, there may be mentioned styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, a-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butyl styrene, p-tert-butylstyrene, p-n-hexylstyrene, p-noctylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methylstyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene and the like.

As examples of the alkyl acrylate monomer which may give the alkyl acrylate monomer component, there may be mentioned methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl oi-chloroacrylate and the like.

As examples of the alkyl methacrylate monomer which may give the alkyl methacrylate monomer component, there may be mentioned methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the like.

Therefore, the above main component resin is composed of a resin obtained by copolymerization of said styrene monomer and a monomer composed of or containing two alkyl acrylate monomers; a resin obtained by copolymerization of said sytrene monomer and a monomer composed of or containing two alkyl methacrylate monomers; or a resin obtained by copolymerization of said styrene monomer and a monomer composed of or containing the alkyl acrylate and methacrylate monomers, and, of these resins, the last one is particularly preferable.

The styrene monomer component is included in the main component resin at 50-90 % by weight and the acrylate monomer component is preferably contained at 10-50 % by weight.

The two monomer components for the acrylate monomer component are contained at a ratio of at least 5 % by weight, respectively. The main component resin constitutes at least 70 % by weight of the binder resin. Illustrative examples of the resin which may be employed in the binder resin together with said main component resin, may include any resins commonly employed for this purpose, e.g., a polyolefin resin, a styrene resin, an acrylic resin, a polyester resin, a phenol resin, an epoxy resin and the like.

As a still another binder resin which may be employed in the present toner, there is mentioned a polyester resin. A polyester resin itself tends to be easily charged negative and can provide a uniform negative charge property with relatively easy availability of its low molecular weight product. Therefore, a toner having a uniform charge property and lower softening point can be obtained by using said polyester resin as a binder, and also can preferably show a better wetting onto a support, e.g., a transfer paper and the like when molten, as compared with a toner containing as a binder a vinyl type polymer and further can accomplish a sufficient fixation at a lower temperature, as compared with a vinyl type polymer toner having an approximately equal softening point.

However, if a sole polyester resin is employed as a binder resin, the resultant toner is apt to show a lower offset-producing temperature and a narrower fixable temperature range. As a result of our studies, it has been found that, when a polyester resin containing a "chloroforminsoluble" in a range of 5-25 % by weight is employed as a binder, there can be given a toner having a higher offset-producing temperature with keeping a softening point as low and thus a broad fixable or fixing temperature range. Namely, a toner having excellent fixing property and offset-preventing effect can be surely provided by the use of said specific polyester resin as a binder. If chloroform-insoluble is of more than 25 % by weight in a polyester resin, a softening point of a toner rises and a fixing temperature accordingly becomes higher.If less than 5 % by weight, there is provided a practically unsuitable toner having a lower offset-preventing property.

The value for "chloroform-insoluble" as shown herein can be determined as follows: Into a 1 50 ml vessel are placed 5.00 9 of a sample powder obtained by finely milling a resin sample and passing through a 40-mesh sieve and 5.00 g of a filter aid "Radiolite #700". After adding 100 g of chloroform, the vessel is placed and rotated over more than 5 hours on the rack of a ball mill to dissolve the sample in chloroform completely. On the other hand, 5.00 g of Radiolite are uniformly precoated over a filter paper No. 2 with a diameter of 7 cm, which is previously placed in a press-filter and adhered to the filter with a small volume of chloroform.

Then, the content of said vessel is poured into the filter and the vessel is washed thoroughly with 100 ml of chloroform. The washing is added to the filter so that any residue may not remain over the wall of said vessel. Then, the filter is closed with its upper cover and filtration is conducted under pressure of not higher than 4 kg/cm2. After dropping of chloroform ceases, residue over the filter paper is washed with 100 ml of fresh chloroform and press-filter is again worked. After completion of the foregoing procedures, the filter paper, residue thereon and all Radiolite are placed on aluminum foil and dried in a vacuum drier for 10 hours under the condition of 80-100"C and 100 mmHg.Then, a total weight "a" (in gram) of the so obtained dried product is weighed and the chloroform-insoluble "X" (% by weight) is calculated according to the following equation: a-(weight of filter paper)-(weight of Radiolite) X x100 Sampling weight As the polyester resin which may be employed in this invention, there may be preferably mentioned those polyester resins having a softening point of 125-145"C, particularly 130-140'C; said softening point being defined as a half of height from effusion starting point till effusion end point when 1 cm3 of a sample is molten and effused in a flow tester (manufactured by Shimazu Corporation) under the conditions of die thin hole diameter or 1 mm, pressure of 20 kg/cm2 and temperature rising rate of 6 C/min. Further, there may be preferably employed those polyester resins having a glass transition point of not less than 55"C, particularly 60"C or higher, as measured by a differential scanning calorimeter (manufactured by Rigaku Denki K.K).

The present toner may include in said binder resin a coloring agent and, if required, a property-improving agent and a magnetic material.

As examples of the coloring agent, there may be mentioned carbon black, Nigrosine dyes (C.l.

No. 5041 SB), Aniline Blue (C.l. No. 50405), Calcoil Blue (C.l. No. azeoc Blue), Chrome Yellow (C.l. No. 14090), Ultramarine Blue (C.l. No. 77103), Du Pont Oil Red (C.l. No. 26105), Quinoline Yellow (C.l. No. 47005), Methylene Blue Chloride (C.l. No. 52015), Phthalocyanine Blue (C.l. No. 74160), Malachite Green Oxalate (C.l. No. 42000), Lamp Black (C.l. No.

77266), Rose Bengale (C.l. No. 45435), a mixture thereof and the like. The coloring agent should be included in a sufficient ratio to form a visible image with a sufficient concentration, usually at about 1 to 20 parts by weight to 100 parts by weight of the binder.

Where carbon black is to be employed as a coloring agent, acidic carbon black is particularly preferable because of triboelectric charge characteristics of a toner and a good dispersability in the binder. The term "acidic carbon black" as used herein is meant to indicate such a carbon black which shows a pH value of not more than 5.0 supernatant obtained after a sample is boiled in water and allowed to stand.

As examples of the magnetic material, there may be mentioned a ferromagnetic material such as iron, cobalt, nickel, an alloy thereof or a compound containing said elements such as ferrite or magnetite; a metal alloy containing no ferro-magnetic element, but capable of having a ferromagnetic property such as alloys called Heusler's alloy containing manganese and cupper, e.g., Mn-Cu-Al, Mn-Sn-Cu and the like; chromium dioxide; and others. The magnetic material is usually and uniformly dispersed in the binder in the form of a fine powder having an average particle diameter of 0.1-1 ,um and may be included at 20-70 parts by weight, preferably 40-70 parts by weight, per 100 parts by weight of a toner.

As examples of-said property-improving agent, there are mentioned a charge-controlling agent, an offset-preventing agent, a fluidity-improving lubricant and so on. However, the present toner itself has good properties as a toner and then said property-improving agent, if used, may be-added in a minor amount. For instance, as the offset-preventing agent or a releasing agent, there may be mentioned a polyolefin having a softening point of 80-180"C by a ring and ball method; a fatty acid, a metal salt thereof and a fatty acid amide; and the like. The offsetpreventing agent may be added, for example, at 1-10 % by weight preferably 1-5 % by weight to the binder.

Moreover, an external additive may be further added to the present toner. As examples of said additive, a hydrophobic silica fine powder or a fluororesin powder may be added to the toner at 0.1-1.2 % by weight for improving fluidity and a lubricant, e.g., a fatty acid or a fatty acid metal salt may be added at not more than 2.0 % by weight for improving cleaning property.

Carrier As the carrier for the present developer, there is mentioned a carrier core material covered with a coating resin.

As the coating resin, there may be employed any copolymers or terpolymers which contain a styrene component derived from a styrene monomer, preferably copolymers or terpolymers of sytrene with an alkyl acrylate or methacrylate. It is also preferable that this coating resin has a glass transition point of not less than 50"C and a softening point of 80-250"C. The styrene component is preferably inluded in the coating resin at a ratio of 30-90 % by weight, but if a styrene component is at a higher ratio, durability and dependence relative humidity can be improved as also seen in the binder resin. However, when more than 90 % by weight is applied, a coating property becomes reduced and a coating film once adhered to the carrier core material becomes peeled away.

As the core material for carrier, there may be applied any materials and magnetic materials such as iron, ferrite or magnetite may be preferably employed. Further, particle of the material is preferably of a spherical shape. A thickness of the coating film with said coating resin is usually 0.5-5,um preferably 1.0-3.0 ym.

In this embodiment, a particle diameter of the carrier is an average particle diameter upon particle size volume distribution of 50-120 120,um, preferably 60-100 .

Also, it should be noted that the carrier for the present developer is composed of particles, whose average particle diameter upon particle size volume distribution is in the range of 50-120,um, preferably 60-100 jm. With regard to its particle diameter distribution, it is preferable that particles with a diameter of not more than 40,um are present at not more than 4 % and those with a diameter of not less than 1 30 ym are present at not more than 30 % upon particle size volume distribution.Because of the aforesaid average particle diameter, a ratio of the whole surface area of a toner particle to that of a carrier particle is adapted to be appropriate so that a preferable, stable Q/M value may be given in a toner and a good visible image with a high image density can be formed over many times. When the average particle diameter is less than 50 ym, a stable charge property may be obtained, but carrier particles tend to adhere onto a photoreceptor. If the diameter is more than 1 20 clam, a preferable triboelectric charge characteristics could not be attained, visible image with a poor quality is formed together with a greater change in Q/M upon change in toner concentration and thus no stable development can be accomplished at all.

As another embodiment of the carrier, it is composed of particles having the above specified average particle diameter upon particle size volume distribution and comprising polyhedron particles. The polyhedron particle of this carrier is, as illustrated in Fig. 1, as a whole of an approximately speherical or oval-like shape and the outer surface thereof is formed with a number of flat surfaces or nearly flat, slightly curved surfaces. For instance, the particle can be given by such mechanical treatment of spherical particles, amorphous particles or porous surface particles made of a metal or alloy by collision with a flat surface with a ball mill, a vibrating mill or an attracter.In this embodiment, a whole surface area of the carrier can be considerably increased because of polyhedron particles as carrier particles, as compared with the carrier comprising spherical particles with approximately equal particle diameter. In addition, the carrier has the above-specified average particle diameter, increase in the whole surface area of a toner with reduced particle diameter of the toner can be compensated a ratio of the toner whole surface area to the carrier whole surface area can be brought to a preferable range and thus a favourable charged state can be always given upon a toner and a broad toner concentration range allowable for the developer can be available. Therefore, visible image with a usually stable image quality can be produced togehter with a sufficient durability as a developer.After all, visible image with a high quality can be surely and many times formed upon the aforesaid toner properties. The material for this carrier may be any of the above-mentioned ones, but a metal or alloy is preferable upon easy formation of polyhedron particle, i.e., easiness in converting a material particle to polyhedron particle by a mechanical treatment as explained above. In fact, iron is most preferable in view of easy availability of the raw material, easy production and low expense. Then, polyhedron particle formed by mechanical treatment of iron powder material may be preferably employed in this embodiment. As iron powder materials, there may be used inexpensive amorphous or porous iron powder, since iron powder particles are as a whole of a uniform shape and a smooth surface by mechanical treatment.However, this is not to prevent the use of a relatively expensive spherical iron powder as an iron powder material.

Where a carrier is electroconductive, charge in electrostatic image to be developed, when contacted therewith, is undesirably apt to leak out. Then, it is preferable to form a resin coating layer over the outer surface of a polyhedron particle composed of iron, other metal or an alloy as stated above. By using such an insulating carrier, toner filming of a carrier particle having adhered a toner particle over the surface thereof can be prevented, triboelectric charge characteristic of a carrier to a toner becomes stable to increase durability and thus the present effects as previously stated are much more established and increased.As examples of the resin to form said resin coating layer, there may be mentioned a homopolymer obtained by polymerization of a monomer, e.g., a styrene, e.g., p-chlorostyrene, methylstyrene; a vinyl halide, e.g., vinyl chloride, vinyl bromide, vinyl fluoride; a vinyl ester, e.g., vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; an a-methylene aliphatic mono-carboxylic acid ester, e.g., methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 3-chloroethyl acrylate, phenyl acrylate, methyl a-chloroacrylate, melthyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylo-nitrile, acrylamide; a vinyl ether, e.g., vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether; a vinyl ketone, e.g. methyl isopropenyl ketone; or other resins such as an epoxy resin,na rosin-modified phenol-formalin resin, a cellulose resin, a polyether resin, a polyvinyl butyral resin, a polyester resin, a styrenebutadiene resin, a polyurethane resin, a vinyl formal resin, a melamine resin, a polycarbonate resin, a fluorocarbon resin (e.g. Teflon), alone or in combination therewith. Of these resins, a styrene-acrylic type resin (e.g. styrene-methyl methacrylate, styrene-butyl methacrylate), an epoxy resin, a styrene-butadiene resin, a butyral resin, a cellulose resin are particularly preferable.

According to the present developer, there are specific requirements on particles of atoner and a carrier as stated above and a stable, favourable triboelectric charge characteristics can be attained therein. Therefore, there is no need to add any charge controlling agent to a toner or restriction of its content to a less range, a highly sharp and gradient visible image with a high resolving power can be produced without any gray background and further advantageous development of electrostatic image can be accomplished without any actual harmful effects.

This invention will be more concretely ilustrated by way of the following examples, but they are not intended to be limiting this invention thereto, Example 1 One hundred parts by weight of a styrene-methl methacrylate-butyl acrylate copolymer resin (glass transition point of 86 C, softening point of 132 C) composed of 80 % by weight of a styrene component, 5 % by weight of a methyl mlethacrylate component and 1 5 % by weight of an n-butyl acrylate component, 1 5 parts by weight of acidic carbon black "Morgal L" (pH 3.0, manufactured by Cabbot Co., Ltd.) and 5 parts by weight of polypropylene "Viscol 660P" (manufactured by Sanyo Chemical Industries, Ltd.) were pre-mixed for 1 5 minutes by Henschel mixer, molten and mixed by an extruder and, after cooling, coarsely milled and then finely milled by a jet mill. The resulting powder was classified by a classification machine to form a toner powder having an average particle size of 9.0 m upon particle size volume distribution.

Then 0.8 % by weight of a hydrophobic silica fine powder "Aerosil R972" (manufactured by Nippon Aerosil K.K.) was added thereto, thereby forming a toner.

On the other hand, a styrene-methyl methacrylate copolymer resin of 65 % by weight of a styrene component and 35 % by weight of methyl methacrylate was coated with a thickness of about 2,um over a carrier core material composed of iron powder having an average particle size of 98,um to prepare a carrier.

Twenty grains of the above-mentioned toner were admixed with 1000 9 of the abovementioned carrier to produce the present developer, which is designated as Sample 1.

The Sample 1 was charged into the developing part in an elctrophotographic copying machine "U-Bix 3000" (manufactured by Konishiroku Photo Ind. Co., Ltd.) and a triboelectric charge-to-mass ratio (Q/M) after stirring for 1 minute was measured by a blow-off method to show the initial Q/M of 24.3 lLC (coulomb)/g. Thereafter, copying tests were carried out to produce a good copying image having a high image density of the maximum image density Dmax of 1.45 and a sharp resolving power of 8 lines/mm without any gray bakcground. Further, after copying running over 20,000 times, a reduction in Q/M of the present developer to the initial Q/M was so much small as 1.25 %.

Comparative Example 1 The same procedure as in Example 1 except that acidic carbon black was employed in an amount of 5.0 parts by weight were repeated to produce a toner having an average particle size of 9.2 ,um. On the other hand, the same procedures as in Example 1 except that a styrenemethyl methacrylate copolymer resin of 60 % by weight of a styrene component and 40 % by weight of a methyl methacrylate component was employed as a coating resin were repeated to produce a carrier. By employing the toner and carrier, a comparative developer was prepared according to the same procedures as in Example 1. It is designated as Comparative Sample 1.

The Comparative Sample 1 was tested in a similar manner to Example 1 to show the initial Q/M of 25.8,uC/g, the maximum image density Dmax in copying image of 1.24, the resolving power of 5 lines/mm and the reduction in Q/M of 10.1 % after 20,000 times copyings.

It is apparent from the above results that the Comparative Sample 1 can provide a relatively high image density, but shows a lower sharpness with a reduced resolving power. In fact, broken lines of a letter part were observed in a copying image.

Example 2 According to the same procedures as in Example 1, 100 parts by weight of a styrene-n-butyl acrylate copolymer resin (glass transition point of 63"C, softening point of 129.5"C) of 75 % by weight of a styrene component and 25 % by weight of an n-butyl acrylate component, 25 parts by weight of acidic carbon black "MA-8" (pH 2.5, manufactured by Mitsubishi Chemcial Industries Ltd.) and 3.5 parts by weight of polypropylene "Viscol 660P" (manufactured by Sanyo Chemical Industries, Ltd.) wre employed to produce a toner powder having an average particle size of 10 elm and 0.4 % by weight of a hydrophobic silica fine powder "Aerosil R-972" (manufactured by Nippon Aerosil K.K.) was added thereto, thereby producing a toner.

Then, the present developer having a toner concentration of 2.0 % was prepared from said toner and the carrier as prepared in Example 1. It is designaed as Sample 2.

Similar tests on the Sample 2 as in Example 1 showed a sharp copying image without any gray background with the initial Q/M of 26.8 C/g, the maximum image density in copoying image of 1.40, the resolving power of 8 lines/mm and the reduction in Q/M after 20,000 times copyings of 4.3 %, all of which are excellent.

Comparative Example 2 The same procedures as in Example 2 except that acidic carbon black was employed in an amount of 34 parts by weight were repeated to produce a toner. On the other hand, the same procedures as in Example 1 except that a styrene-methyl methacrylate copolymer of 70 % by weight of a styrene component and 30 % by weight of a methyl methacrylate component were repeated to produce a carrier. A comparative developer having a toner concentration of 2 % was prepared from said toner and carrier. It is designated as Comparative Sample 2.

Similar tests on the Comparative Sample 2 as in Example 1 showed that the initial Q/M was 22.8 C/g but a reduction in Q/M after 20,000 times copyings was as large as 37.1 % and thus a copying image became poor as the number of copying times increased.

Example 3 to 5 A terpolymer (glass transition point of 66"e, softening point of 136"C) of 70 % by weight of a styrene component, 10 % by weight of a methyl methacrylate component and 20 % by weight of an n-butyl acrylate component was employed as a binder resin. 100 parts by weight of said terpolmer were premixed with 1 5 parts by weight of each of three types of carbon black as indicated in the following Table 1 for 1 5 minutes by i Henschel mixer, molten and mixed by an extruder and, after cooling, finely milled and classified to produce a total 3 types of toner having an average particle size of about 9.0,zm.

Table 1 Acidic Carbon Black Manufacturer pH Ex. 3 Morgal L Cabbot 3.0 Ex. 4 MA-8 Mitsubishi Chemical 2.5 Ex. 5 RAVEN 5250 Columbia Carbon 2.0 From the toners of Examples 1 to 3 and the same carrier as in Example 1 were prepared 3 types of the present developer, each having a toner concentration of 2 %. They are designated as Samples 3 to 5, respectively.

The Samples 3 to 5 were subjected to copying tests with an electrophotographic copying machine "U-Bix 3000" for initial Q/M, maximum image density Dmax and resolving power.

Moreover, a small amount of each toner of the Samples 3 to 5 was molten on an object glass and covered with a cover glass to form a toner layer. Dispersed state of carbon black was examined by its transmission microscope observation. The results are summarized in the following Table 2.

Table 2 Initial Resolving Dispersa Q/M power bility of pH of C.B.* (yC/g) Dmax (line/mm) C.B.

Sample 3 3.0 24.2 1.42 8 Good Sample 4 2.5 25.8 1.45 8 Sample 5 2.0 25.6 1.38 8 * "C.B." means carbon black and will be referred to hereinbelow.

Comparative Examples 3 to 5 According to the same procedures as in Examples 3 to 5 except that there were employed as a carbon black for preparing a toner those indicated in Table 3, there were prepared 3 types of a toner.

Table 3 C.B. Manufacturer pH Comparative Ex. 3 #44 Mitsubishi Chemical 7.5 " " 4 #45 ,, 8.0 " " 5 *30 ,, 9.0 On the other hand, a carrier was prepared according to the same procedures as in Example 1 except that there was employed as a coating resin a styrene-methyl methacrylate copolymer of 30 % by weight of a styrene component and 70 % by weight of a methyl methacrylate component. In the same manner as in Examples 3 to 5, comparative developers were prepared with said toners and carriers and are designated as Comparative Samples 3 to 5, respectively.

Same tests as in Examples 3 to 5 were conducted on the Comparative Samples 3 to 5. The results are summarized in Table 4.

Table 4 Initial Resolving Dispers pH of Q/M power ability of C.B. OLC/g) Dmax (line/mm) C.B.

Comparative slightly Ex. 3 7.5 22.1 1.27 6 poor 4 4 8.0 20.7 1.18 4 5 5 9.0 21.0 1.11 4 Poor As apparent from the results in Tables 2 and 4, present developer can provide preferable triboelectric charge characteristics as well as a high image density and a high resolving power.

Examples 6 and 7 Two toners were prepared according to the same procedures as in Example 1 except that a styrene-methyl methacrylate copolymer of a weight ratio of a styrene component/a methyl methacrylate component of 85/15 (Resin A) and another copolymer with a weight ratio of 50/50 (Resin B) were employed as a binder resin.

Two types of the present developer having a toner concentration of 1.7 % were prepared with said toner and the same carrier as in Comparative Examples 3 to 5 and are designated as Samples 6 and 7.

Comparative Example 6 A toner was prepared in the same manner as in Examples 6 and 7 except that a styrenemethacrylate copolymer (Resin C) with a weight ratio of a styrene component/a methyl methacrylate component of 30/70 was employed as a binder resin for a toner and then a comparative developer was prepared and is designated as Comparative Sample 6.

Initial Q/M was measured on each of the above Samples 6 and 7 and Comparative Sample 6 under the condition I of a temperature of 20"C and a relative humidity of 50 % and the condition II of a temperature of 35'C and a relative humidity of 80 %. The results are summarized in Table 5. It is noted that the developer from the toner using as a binder resin the Resin C of a minor component of styrene showed greatly reduced triboelectric charge characteristics under the condition II of higher temperature and humidity.

Table 5 Initial Q/M 4tC/g) Binder resin for toner Condition I Condition II Sample 6 Resin A 31.3 26.9 " 7 Resin B 28. 6 20.4 Comparative Sample 6 Resin C 24.6 11.8 Copying tests on the Samples 6 and 7 and Comparative Sample 6 were conducted under the same conditions I and II as above by means of an electrophotographic copying machine "U-Bix 3000" and copy images thus formed were evaluated. The results are summarized in Table 6. In case of the Comparative Sample 6, there can be seen a lower resolving power upon gray background. In each column of Table 6, the upper figure indicates the value under condition I and the lower figure does that under condition II.

Table 6 Gray Resolving power Dmax background (line/mm) Sample 6 1.28 0.00 8 1.24 0.00 6 " 7 1.25 0.00 6 1.09 0.01 5 Comparative 1.26 0.01 4 Sample 6 0.98 0.02 4 Example 8 One hundred parts by weight of a terpolymer (glass transition point of 62"C, softening point of 130.5'C) composed of a sytrene component, a methyl methacrylate component and an nbutyl acrylate component at a ratio of 75:5; 20, 15 parts by weight of carbon black "*52" (manufactured by Mitsubishi Chemical Industries Ltd.) and 3 parts by weight of polypropylene "Viscol 660P" were pre-mixed for 1 5 minutes in a Henschel mixer, molten and mixed with an extruder and, after cooling, coarsely milled and finely milled and then classified to prepare 4 types of the toner particles having the distribution indicated in Table 7 with varying the procedures for finely milling and classifying. To each toner was added 0.8 % by weight of a hydrophobic silica fine powder "Aerosil R-972" to prepare two toners meeting the present conditions, namely Sample Toners 1 and 2, and other two toners not meeting the present conditions, namely Comparative Toners 1 and 2.

Table 7 N," N2*** MRT (cm)* (% by weight) (% by weight) Comparative Toner 1 5.5 16.0 0 Sample Toner 1 6.7 9.2 0.2 Sample Toner 2 8.8 6.8 1.2 Comparative Toner2 11.3 4.3 3.1 MRT: Average particle size of toner upon volume distribution **N1: Ratio of fine particle having particle size of less than 5,um to whole toner particles ***N2:Ratio of particle having particle size of not less than 1 6 ym to whole toner particles On the other hand, a carrier core material of iron powder was coated with a styrene-methyl methacrylate copolymer of a styrene component and a methyl methacrylate component at a ratio of 50:50 to prepare a carrier having an average particle diameter (MRC) of 98 Sum upon volume distribution. 2 % by weight of each of the Sample Toners 1 and 2 and the Comparative Toners 1 and 2 were mixed with 100 parts by weight of the above-mentioned carrier to prepare the present developers, namely Samples 8 and 9 and Comparative Samples 7 and 8, respectively.

Each of these developers was charged into a developing part in an electrophotographic copying machine "U-Bix 3000" and, after stirring for 1 minute, initial charged volume of the developer was measured. Copying image thus formed was evaluated by a copying test and also copy runnings over 20,000 times were conducted to observe a toner scattering degree and a change in charged volume of the developer to initial Q/M. The results are summarized in Table 8.

Table 8 Comparative Sample Sample Comparative Sample 7 8 9 Sample 8 Initial Q/M 4tC/g) 38.2 28.6 25.6 20.3 Resolving power (line/mm) 8 8 8 4 Dmax 1.14 1.23 1.31 1.36 Gray background Great None None Slight Toner scatter ,, ,, ,, None Change in Q/M " Great It is apparent from the above results that the present developer can exert excellent effects.

Example 9 According to the procedures as in Example 8, carrier core materials having various particle diameters were employed as a core material to prepare 4 carriers having MRC's of 48 elms 66 ,um, 98 calm and 135 clam, respectively.

In the same manner as in Example 8, developers were prepared from said carriers and the Sample Toner 2 and each developer was tested for initial Q/M, resolving power, Dinax and adhesion of carrier onto the photosensitive drum surface after 20,000 times copyings. The results are summarized in Table 9.

Table 9 Comparative Sample Sample Comparative Sample 9 10 11 Sample 10 MRC (ym) 48 66 98 135 Initial Q/M (FC/g) 20.8 24.3 26.5 32.0 Resolving power (line/mm) 8 8 8 4 Dinax 1.32 1.30 1.30 1.14 Adhesion of carrier Great None None None It will be noted from the above results that only the carrier meeting the present conditions could provide favourable results.

Example 10 In the same manner as in Example 8, 100 parts by weight of a styrene-2-ethylhexyl acrylate copolymer of a styrene component and a 2-ethylhexyl acrylate component at a ratio of 80:20 and 9 parts by weight of carbon black "RAVEN 3500" (manufactured by Columbia Carbon Co., Ltd.) were treated to prepare toner particles having an average particle diameter of 9.2 'lem upon volume distribution, a ratio of fine particles N, with less 5,um of 4.4 % by weight and a ratio of large diameter particles with more 16 elm of 0.8 % by weight. 0.4 % by weight of a hydrophobic silica fine powder "Aerosil R-972" was added to said toner particles to prepare the toner meeting the present requirements.

On the other hand, carrier core materials composed of iron powders with various particle diameters were coated with a styrene-methyl methacrylate copolymer of a styrene component and a methyl methacrylate component at ratio of 40:60 to prepare two carriers having MRC's of 66 clam and 135 cm upon volume distribution, respectively. Developers with various concentrations were prepaed from said carriers and toners and each initial charged volume was measured in the same manner as in Example 8. The results are summarized in Table 10.

Table 10 MRC Toner concentration Initial Q/M Developer (yam) (% by weight) C/g) A 1.0 24.3 B ' 66 2.0 22.6 C 3.0 20.7 D 4.0 20.1 E 1.0 39.8 F 2.0 33.8 G 135 3.0 26.5 H 4.0 21.2 As apparent from the above results, large change in initial Q/M observed upon change in toner concentration when the MRC of the carrier is more than 120 cm. Thus, it is noted that the developer meeting the present conditions can provide a stable triboelectric change to mass ratio, taking into consideration increased toner concentration from repeated developments which are requisite in development with a two component-system developer.

Example 11 The present developer was prepared by admixing 5 parts by weight of the Sample Toner 1 in Example 8 with 100 parts by weight of a carrier composed of iron oxide powder "EFV" (manufactured by Nippon Teppun K.K.) having an average particle diameter of 65 jm upon volume distribution.

Initial Q/M of this developer was measured in the same manner as in Example 8 to show 24.8,uC/g, copy running test over 20,000 times produced a highly sharp visible image without any gray background and reduction in Q/M after 20,000 times copying was only 20.3,uC/g.

Examples 12 to 14 Three resins having a styrene component, a methyl methacrylate component and a n-butyl methacrylate component at the ratio indicated in Table 11 were prepared from styrene, methyl methacrylate and n-butyl methacrylate. The softening point (SP) and glass transition point (Tg) thereof are also shown in Table 11, wherein "St" represent a styrene component, "MMA" a methyl methacrylate component and "n-BMA" a n-butyl methacrylate component.

Table 11 Ratio of monomer components (by weight) SP Tg Resin St MMA n-BMA ( C) (C) Resin 1 50 20 30 132 61 " 2 75 10 15 128 65 " 3 80 5 15 127 63 One hundred parts by weight of each of the Resins 1 to 3 as a binder resin, 10 parts by weight of carbon black "Morgal L" and 3 parts by weight of a low softening point polypropylene "Viscol 660P" were pe-mixed for 1 5 minutes in Henschel mixer, molten and mixed with an extruder and, after cooling, coarsely milled and finely milled and then classified to prepare 3 types of the present toner having an average particle diameter of about 9.2 'lem.

They are designated as Toners 3 to 5, respectively.

To each of the Toners 3 to 5 was added 0.8 % by weight of a hydrophobic silica fine powder "Aerosil R-972" and 2 parts by weight of the resulting mixture were mixed with 100 parts by weight of a resincoated carrier having an average particle diameter of about 100 ym to prepare 3 developers.

Comparative Examples 7 to 10 Four resins composed of only a styrene component and a n-butyl methacrylate component at the ratio indicated in Table 12 were prepared by copolymerization of styrene with n-butyl methacrylate. Their properties are also shown in Table 1 2.

Table 12 Ratio of monomer components (by weight) SP Tg Resin St n-BMA ( C) ('C) Comparative Resin 1 75 25 139 57 " 2 70 30 140 55 " 3 60 40 131 49 " 4 55 45 121 46 In the same manner as in Examples 12-14, the Comparative Resins 1 to 4 were employed as a binder resin to prepare Comparative Toners 3 to 6 and subsequently developers therefrom.

Unfixed toner image was produced with the developers in the above Examples 1 2 and 14 and Comparative Examples 7 to 10 by means of an electrophotographic copying machine "U-Bix 3000" and then fixed by the use of a fixing tester manufactured from the fixing part of an electrophotographic copying machine "U-Bix V" to determine the fixable lowest temperature T1 and the lowest temperature for offset production T2. Also, Q/M and shelf life of the toner to be employed for development were examined. Shelf life was determined by observing if blocking or aggregation may be produced when a toner is placed over 7 days in a thermostat at a temperature of 55"C and a relative humidity of 55%. The results are summarized in Table 1 3.

Table 13 Q/M T1 T2 Toner (iLC/g) ("C) ('C) Blocking Toner 3 23.4 160 235 None ,, 4 25.5 160 220 5 5 25.9 155 215 Comparative Slightly Toner 3 23.2 180 200 observed " 4 22.8 180 200 " 5 20.7 160 175 Observed " 6 20.5 150 140 It is apparent from the above results that the present toner has a large Q/M, a good fixing ability, a high non-offset property, a broad range of fixable temperature at preferable temperature and an excellent shelf life.

Actual copying tests over 10,000 times were carried out with the Toners 3 to 5 by means of an electrophotographic copying machine "U-Bix V3000" (Konishiroku Photo Ind. Co., Ltd.) to produce favourable copy images till tests were completed.

On the contrary, the Comparative Toners composed of the Comparative Resins of only two monomer components showed a lower non-offset property, no or narrow fixable temperature range, a lower shelf life and a small Q/M.

The same actual copying tests as above were also effected with said Comparative Toners 3 to 6. It was seen from these tests that a good quality of copy image was oserved, but rollers in fixing part became contaminated and considerable winding of a transfer paper around rollers was produced and thus these toners are not practically applicable.

Example 15 The resins composed of a styrene component, a methyl methacrylate component and a n-butyl acrylate component at the ratio indicated in Table 14 were prepared by copolymerization of styrene, methyl methacrylate and n-butyl acrylate. The properties of this Resin 4 are also shown in Table 14, wherein "n-BA" represents n-butyl acrylate.

Table 14 Ratio of monomer components (by weight) SP Tg Resin St MMA n-BA ( C) ( C) Resin 4 75 10 15 132 64 Following the same procedures as in Examples 1 2 to 14 except that the Resin 4 was employed as a binder resin, the Toner 6 according to this invention having an average particle diameter of 8.8 clam was prepared and then a developer was prepared therefrom.

Comparative Examples 11 to 12 Two resins composed of only a styrene component and a n-butyl acrylate component at the ratio indicated in Table 1 5 were prepared by copolymerization of styrene with n-butyl acrylate.

Their properties are also shown in Table 1 5.

Table 15 Ratio of monomer components (by weight) SP Tg Resin St n-BA ( C) ( C) Comparative Resin 5 85 15 153 61 " 6 80 20 133 49 Following the same procedures as in Examples 1 2 to 14 except that these Comparative Resins 5 and 6 were employed as a binder resin, Comparative Toners 7 and 8 having an average particle diameter of 8.8 calm were prepared and then developers were prepared therefrom.

Using the developers obtained in the above Example 1 5 and Comparative Examples 11 and 12, shelf life was examined by determining the fixable lowest temperature T, and the lowest temperature for offset production T2. The results are summarized in Table 16.

Table 16 T1 T2 Toner ("C) ("C) Blocking Toner 6 160 230 None Comparative Toner 7 190 200 " " 8 150 160 Observed Example 16 The resin having a high molecular weight portion and a low molecular weight portion, composed of a styrene component, a methyl methacrylate component and a 2-ethylhexyl acrylate component was prepared by copolymerization of styrene, methyl methacrylate and 2ethylhexyl acrylate. The properties thereof are also shown in Table 17, wherein "2-EHA" represents 2-ethylhexyl acrylate.

Table 17 Ratio of monomer components (by weight) SP Tg Resin St MMA 2-EHA ( C) ( C)m Resin 5 75 10 15 130 60 Following the same procedures as in Examples 12 to 14 except that the Resin 5 was employed as a binder resin, the Toner 7 according to this invention with an average particle diameter of 9.2 calm was prepared and then a developer was prepared therefrom.

Comparative Example 13 The resin, which was composed of only a styrene component and a 2-ethylhexyl acrylate component at the ratio indicated in Table 18 and had a softening point (SP) approximate to that of the Resin 5 in Example 16, was prepared by copolymerization of styrene with 2-ethylhexyl acrylate. The properties thereof are also shown in Table 1 8.

Table 18 Ratio of monomer components (by weight) SP Tg Resin St 2-EHA ( C) ( C) Comparative Resin 7 85 15 129 45 Following the same procedures as in Examples 12-14 except that this Comparative Resin 7 was employed as a binder resin, the Comparative Toner 9 having an average particle diameter of 9.2 ym was prepared and then a developer was prepared therefrom.

Using the developers obtained in the above Example 1 6 and Comparative Example 13, shelf life was examined by determining the fixable lowest temperature T1 and the lowest temperature for offset production T2. The results are summarized in Table 1 9.

Table 19 T1 T2 Toner ("C) ("C) Blocking Toner 7 160 215 None Comparative Toner 9 160 180 Observed Examples 17 and 18 and Comparative Examples 14 and 15 One hundred parts by weight of a terpolymer (glass transition point of 64"C, softening point of 132"C), which has a high molecular weight portion of a styrene component, a methyl methacrylate component and a n-butyl acrylate component at a ratio of 75:5:20 and a low molecular weight portion of said three components at a ratio of 70:20::10, 10 parts by weight of carbon black "Morgal L" and 3 parts by weight of a low softening point polypropylene "Viscol 660P" were pre-mixed for 15 minutes in a Henschel mixer, molten and mixed with an extruder and, after cooling, coarsely milled and finely milled and then classified to prepare 4 types of toner particles, the distribution of which will be indicated in Table 20, by varying the procedures for fine milling and classifying. To each toner particle type was added 0.8% by weight of a hydrophobic silica fine powder "Aerosil R-972" to prepare two Toners 8 and 9, which satisfy the present conditions, and two Comparative Toners 10 and 11, which do not satisfy the present conditions.

Table 20 N1 N2 Toner MRT 4lem) (% by weight) (% by weight) Comparative Toner 10 5.1 18.0 0 Toner 8 7.2 8.8 0.2 " 9 9.2 6.0 1.1 Comparative Toner 11 11.5 2.8 3.5 In Table 20, "MRT", "N," and "N2,, are as defined above.

On the other hand, an iron powder core material for a carrier was coated with a styrene-methyl methacrylate copolymer having a ratio of a styrene component to a methyl methacrylate component of 50:50 to prepare a carrier having the MRC of 98,um upon particle size volume distribution. 2% by weight of each of the Toners 8 and 9 and Comparative Toners 10 and 11 were admixed with 100 parts by weight of said carrier to prepare Samples 1 2 and 1 3 and Comparative Samples 11 and 12, respectively.

These developers were tested in the same manner as in Example 8. The results are summarized in Table 21.

Table 21 Comparative Sample Sample Comparative Sample 11 12 13 Sample 12 Initial Q/M (uC/g) 39.4 27.3 23.8 19.6 Resolving power (line/mm) 8 8 8 4 Dmax 1.06 1.25 1.32 1.35 Gray background Great None None Slight Toner scatter ,, " ,, None Change in Q/M ,, Slight Slight Great It is apparent from the above results that a large Q/M can be given and a highly sharp copy image with a high quality and resolving power can be produced many times by using the present toner which meets the specific conditions, especially with regard to particle diameter.

Example 19 A polyester resin having a chloroform-insoluble content of 12% by weight and a softening point of 130"C was prepared by reacting 270 9 of 1,4-butanediol, 150 9 of terephthalic acid and 231 9 of benzene-1,2,4-tricarboxylic acid at 200 C.

One hundred parts by weight of the polyester resin as a binder resin, 1 3 parts by weight of carbon black "MA-8" (manufactured by Mitsubishi Chemical Industries Ltd.), 3 parts by weight of polypropylene "Viscol 660P" and 1 part by weight of a fatty acid amide was "Hoechst Wax C" (manufactured by Hoechst A.G.) were pre-mixed in a Henschel mixer, molten and mixed with an extruder, cooled, coarsely milled and then finely milled to prepare a toner powder.

This toner powder was classified by means of a zigzag classification machine (manufactured by Alpine Co., Ltd.) to prepare two toners which satisfied the particle diameter conditions of this invention, namely Toners 10 and 11 and also three toners which did not satisfy said conditions, namely Comparative Toners 12, 1 3 and 14.

Particle diameter distributions of such toners are shown in Table 22.

Table 22 MRT N1 N2 Toner m) (% by w.) (% by w.) D m) Toner 10 7.5 11.0 0.2 5.04- 6.35 11 11 9.6 3.6 1.6 6.35- 8.00 Comparative Toner 12 6.2 24.8 0 4.00- 5.04 13 10.2 2.4 3.2 6.35- 8.00 " 14 11.3 1.1 6.5 8.00-10.08 In this Table, MRT, N1 and N2 are as defined above and D means particle diameter range including the greatest number of particles according to Coulter Counter "Model TA II".

Two parts by weight of each of these 5 Toners were admixed with 100 parts by weight of a resin-coated carrier having an average particle diameter of 100,um to prepare five developers, namely Samples 14 and 15 and Comparative Samples 13, 14 and 15, respectively.

Each Sample was subjected to copy test over 10,000 times by means of an electrophotographic copying machine "U-Bix 3000". Copy image after 10,000 times copyings was evaluated for Dmax, resolving power and degree of scavenging mark on the developing image and also record of copy test was examined for inferior cleaning, gray background and toner scatter as well as fluidity of a toner at the beginning of application.

Scavenging mark (or brush mark) on the developing image was evaluated upon the results from determination of white area in solid portion by means of "Areaduck" (manufactured by Konishiroku Photo Ind. Co., Ltd.) and toner fluidity was evaluated upon Aerated bulk density value measured by means of "Tapdenser" (Seishin Kigyo K.K.). The results are summarized in Table 23.

Table 23 (1) Scavenging Resolving mark on the Gray power developing back Developer Dmax (line/mm) image (%) ground Sample 14 1.12 8 1.7 None 15 15 1.21 8 2.5 Comparative Sample 13 1.08 8 1.4 Great ,, 14 1.24 6 4.3 None 15 1.15 4 5.2 Table 23 (2) Toner Developer Inferior cleaning scatter Fluidity Sample 14 None Slight 0.38 15 ,, None 0.42 Comparative Sample 13 Observed Many 0.31 14 14 None None 0.43 " 15 " ,, 0.45 As apparent from the above results, all the present toners are excellent in image properties and also exhibit stable characteristics in many times image formings.On the contrary, the Comparative Sample 13 containing a large amount of particles with a small particle diameter presents problems in cleaning, gray background, toner scatter and toner fluidity, while the Comparative Samples 14 and 15 present problem in image property.

Example 20 A polyester resin having a chloroform-insoluble content of 8% by weight was prepared by reacting 299 9 of terephthalic acid, 211 9 of polyoxypropylene (2,2)-2,2-bis(4-hydroxyphenyl)- propane and 82 9 of pentaerythritol at 200 "C.

One hundred parts by weight of said polyester resin as a binder resin, 10 parts by weight of acidic carbon black "Morgal L", 2 parts by weight of polypropylene "Viscol 660P" and 2 parts by weight of a fatty acid amide wax "Hoechst Wax C" were pre-mixed in a Henschel mixer, molten and mixed with an extruder, cooled, coarsely milled, finely milled and then classified to prepare the pesent toner with an average particle diameter of 9.2 clam, which is designated as Toner 12.

To 2 parts by weight of this Toner 1 2 having incorporated therein 0.8% by weight of a hydrophobic silica fine powder "Aerosil R-972" and 0.2% by weight of zinc stearate were admixed 100 parts by weight of a resin-coated carrier having an average particle diameter of 100 ym to prepare a developer.

Example 21 A polyester resin containing 18% by weight of chloroform-insoluble was prepared in the same manner as in Example 20 except that the reaction period of time was changed and then the present toner having an average particle diameter of 8.8 m (hereinafter referred to as Toner 13) was prepared from said polyester resin according to the same procedures as in Example 20.

Comparative Examples 16 and 17 Two polyester resins containing 2% by weight and 29% by weight of chloroform-insoluble, respectively, were prepared in the same manner as in Example 20 except that the reaction period of time was changed and then two toners having an average particle diameter of 9.2 calm and 9.0,um, respectively, were prepared therefrom, which will be designated as Comparative Toners 1 5 and 1 6. Thereafter, developers were prepared from said toners.

The developers obtained in Examples 20 and 21 and Comparative Examples 1 6 and 1 7 were tested according to the same procedures as in Comparative Examples 7 to 10. The results are summarized in Table 24.

Table 24 (1) Toner T1 ("C) T2 ( C) Tg ("C) SP ("C) Toner 12 160 > 230 61 127 13 13 165 > 230 68 136 Comparative Toner 15 155 195 54 121 16 16 180 > 230 72 151 Table 24 (2) Toner Q/M Aggregation Evaluation Toner 12 26.6 None Good 13 13 28.1 Comparative Toner 1 5 27.2 Observed Bad 16 27.0 None As apparent from the above results, the present toner shows a favourable fixing property, a high offset-preventing effect, a broad fixable temperature range and an excellent shelf life.

Using the Toners 12 and 13, copy test over 10,000 times by means of an electrophotographic copying machine "U-Bix 3000" could produce a good copy image until the test was completed. On the contrary, similar copy tests with the Comparative Toners 1 5 and 1 6 showed that the Comparative Toner 1 5 exhibited a severe offset phenomenon, while the Comparative Toner 1 6 exhibited an insufficient fixation and thus there could be no practically valuable copy images in every instance.

Example 22 The present toner, Toner 14, was prepared in the same manner as in Example 21, while a comparative toner was prepared in the same manner as in Example 21 except that the polypropylene and fatty acid amide wax as releasing agents were omitted. From these toners were prepared two developers, namely Sample 16 and Comparative Sample 16, in the same manner as in Example 21.

The same fixing tests as in Example 20 on such developers were carried out. The results are summarized in Table 25.

Table 25 Developer T, ( C) T2 ( C) Sample 16 165 > 230 Comparative Sample 16 165 180 It is apparent from the above results that a remarkable offset-preventing effect can be accomplished with the addition of a releasing agent in heat roll fixation.

Example 23 A polyester resin "A" containing 17% by weight of chloroform-insoluble was prepared by reacting 299 9 of terephthalic acid, 211 9 of polyoxypropylene (2,2)-2,2-bis(4-hydroxyphenyl) propane and 82 9 of pentaerythritol.

According to a conventional method for preparing a toner comprising the steps of mixing, melting, milling and classifying by the use of 100 parts by weight of the above polyester resin A, 10 parts by weight of carbon black "Morgal L", 2 parts by weight of polypropylene "Viscol 660P" and 2 parts by weight of wax "Hoechst Wax-C", there was prepared the Toner 1 5 which had an average particle diameter on volume distribution of 9.1,us, a particle diameter of the greatest number of particles on numer distribution of 7.1 clam, a ratio N1 of the number of particle with a particle diameter of less than 5 ym to whole particle number of 4.2% and a ratio N2 of the number of particle with a particle diameter of more than 16 clam to whole particle number of 0.1%.

On the other hand, a resin solution prepared by copolymerization of styrene with methyl methacrylate at a weight ratio of 70:30 was sprayed by means of a fluidized bed coating over a carrier material, iron powder "DSP-135C" (manufactured by Dowa Teppun K.K.) having an average particle diameter of 98 clam upon volume distribution and composed of polyhedron particles, thereby forming a resin coating layer with a thickness of about 2,um over said carrier to prepare Carrier A. Then, the present developer, Sample 17, was prepared by admixing 1.176 g of said Carrier A with 24 g of said Toner 1 5.

By the running test over 20,000 times on said Sample 17, by means of an electrophotographic copying machine "U-Bix 3000", there was produced a highly sharp copy image with a high resolving power and copy image at the end of the test was of the same quality as in that at the beginning of the test. Measurement of Q/M at the beginning and end of the test showed to be - 26.8 CLC/g and - 24.8 C/g, respectively, which established that a very stable triboelectric charge could be effected.

Comparative Example 18 A Carrier B was prepared in the same manner as in Example 23 except that spherical iron powder with an average particle diameter of 103,lim on volume distribution (manufactured by Shinto Bureita K.K.) was employed as a carrier material and the same procedures as in Example 23 were then repeated to prepare a developer, Comparative Sample 1 7.

According to the same running test as in Example 23 on this Sample 17, copy image with a high quality was produced at the beginning of the test, but copy image with a poor sharpness, a low resolving power and a deficient practicability, was produced around when copyings reached 10,000 times. Also, toner Q/M was - 28.9 jLC/g at the beginning of the test, but it was reduced to - 23.4 jLC/g at the end of the test with a great change in said volume. Moreover, a remarkable reduction in image density was observed during the running test as copying times became increased, which is believed to be derived from direct influence of change in toner concentration in the developer upon image density.

Further, these results may be construed as spherical carrier being disadvantageous if carriers having an approximately equal particle diameters were employed even with any less particle diameter.

Example 24 A polyester resin "B" containing 12% by weight of chloroform-insoluble was prepared by reacting 1 50 9 of terephthalic acid, 270 9 of 1,4-butanediol and 231 9 of benzene-1.2,4- tricarboxylic acid. In the same manner'as in Example 23 using 100 parts by weight of the above polyester resin B, 1 3 parts by weight of carbon black "#52" and 4 parts by weight of polypropylene "Viscol 660P", there was prepared a toner powder, which was then classified to prepare the toner meeting the requirements for toner particle diameter (Toner 1 6) and two toners not meeting the above requirements (Comparative Toners 1 7 and 18). Particle size volume distribution of such toners is shown in Table 26.

Table 26 MRT N, N2 Toner bm) (% by w.) (% by w.) D m) Toner 16 8.8 2.4 0.9 6.35- 8.00 Comparative Toner 17 6.1 18.2 0 5.04- 6.35 18 18 11.6 0.1 4.1 8.00-10.08 In this Table, MRT, Nt, N2 and D are as defined above.

3 developers having a toner concentration of 2% by weight were prepared by admixing said 3 toners with the same carrier as the Carrier A in Example 23 and subjected to copy tests as stated above. The results are summarized in Table 27.

Table 27 Comparative Comparative Developer Sample 18 Sample 18 Sample 19 Comparative Comparative Toner Toner 16 Toner 17 Toner 18 Q/M (uC/g.) - 27.3 - 35.4 - 20.8 Fluidity Good Bad Good Dmax 1.18 0.83 1.21 Resolving power (line/mm) 8 8 6 Gray background None Observed Observed Scavenging mark on the develop ing image (%) 1.2 0.9 4.6 Then, running tests over 20,000 times on the above 3 developers were effected in the same manner as in Example 23 to evaluate toner and copy image in each developer at the end thereof. The results are summarized in Table 28.

Table 28 Comparative Comparative Developer Sample 18 Sample 18 Sample 19 Change rate of Q/M*(%) 10.2 26.8 16.8 Dmax 1.16 1.11 1.19 Resolving power (line/mm) 8 8 4 Gray background None Observed None Scavenging mark on the develop ing image (%) 1.4 1.1 4.2 *Change rate of Q/M after 20,000 times copyings upon Q/M at the beginning as indicated in Table 27.

As apparent from the above results, the present developer can produce copy image with a high quality, a stable charged state in toner over many times and a large durability.

Example 25 A developer was prepared in the same manner as in Example 23 except that the iron powder "DSP-1 35C" for the Carrier A in Example 23 was applied as such without any resin coating. It will be referred to as Sample 19 hereinafter.

The same running test as in Example 23 on this Sample 1 9 as well as the Sample 1 7 in Example 23 was carried out for change rate in Q/M and copy image at the end of the test. The results are summarized in Table 29.

Table 29 Developer Sample 1 7 Sample 19 Change rate of Q/M (%) 7.5 24.3 Dmax 1.18 1.02 Resolving power (line/mm) 8 5 Slightly Gray background None observed Scavenging mark on the developing image (%) 1.2 2.8 It will be noted from the above results that the carrier having a resin-coating layer can show favourable properties.

Example 26 Following the same procedures as in Example 22 for preparing the polyester resin A except that reaction period of time was changed, there were prepared two polyester resins B and C.

The properties thereof are given with the resin A in Table 30.

Table 30 Chloroform-insoluble Resin (% by w.) SP ("C) Polyester resin A 17 133 " " B 22 138 C " C 4 129 In the same manner as in Example 22, two toners were prepared from said resins B and C and then two developers (Samples 20 and 21) were prepared therefrom.

Fixing tests as stated above were effected on said Samples 17, 20 and 21. The results are summarized in Table 31.

Table 31 Developer Binder in toner T ("C) T ( C) Sample 17 Polyester resin A 1 70 > 230 20 ,, ,, B 180 > 230 " 21 ,, ,, C 155 > 200 It will be noted from the above results that a developer wherein the binder of toner contains an adequate amount of chloroform-insoluble, can give a low fixable lowest temperature and a high offset producing temperature and hence a broad fixable temperature range.

Claims (34)

1. A toner for the development of an electrostatic image which consists essentially of particles having an average particle diameter upon particle size volume distribution within a range of 6 to 10 m and a particle diameter of the greatest number of particles upon particle size number distribution within a range of 5 to 8 clam, the number of particles having a particle diameter of less than 5 ym being not more than 15% of whole particle number and the number of particles having a particle diameter of more than 16 ,um being not more than 2% of whole particle number.

2. A toner according to claim 1, wherein a resin for said toner is a copolymer containing a styrene.

3. A toner according to claim 2, wherein said copolymer is a styrene-alkyl acrylate copolymer or a styrene-alkyl methacrylate copolymer.

4. A toner according to claim 2, wherein said toner further contains a coloring agent.

5. A toner according to claim 4, wherein said coloring agent is acidic carbon black.

6. A toner according to claim 2, wherein said resin is a polyester resin.

7. A toner according to claim 6, wherein said polyester resin contains 5 to 25% by weight of chloroform-insolubles.

8. A toner according to claim 2, wherein said toner further contains a releasing agent.

9. A toner according to claim 8, wherein said releasing agent is a polyolefin having a softening point of 80 to 180"C, a fatty acid amide, a fatty acid or a metal salt thereof.

10. A toner according to claim 9, wherein said polyolefin is polyethylene or polypropylene.

11. A toner according to claim 1, wherein said resin is a copolymer composed of at least 3 monomers.

1 2. A toner according to claim 11, wherein said copolymer is composed of at least one sytrene monomer component and at least two monomer components selected from at least one of an alkyl acrylate and an alkyl methacrylate.

1 3. A toner according to claim 11, wherein said copolymer is composed of at least one styrene monomer component, at least one alkyl acrylate monomer component and at least one alkyl methacrylate monomer component.

14. A developer for electrostatic image which consists essentially of toner particles and a carrier, said toner particles having an average particle diameter upon particle size volume distribution within a range of 6 to 10 ym and a particle diameter of the greatest number of particles upon particles size number distribution within a range of 5 to 8 m, the number of particles having a particle diameter of less than 5 ym being not more than 15% of whole particle number and the number of particles having a particle diameter of more than 1 6 ym being not more than 2% of whole particle number.

15. A developer according to claim 14, wherein said carrier consists essentially of particles having an average particle size upon particle size volume distribution within a range of 50 to 120 jm.

1 6. A developer according to claim 15, wherein said particle is a polyhedron particle.

1 7. A developer according to claim 15, wherein said carrier is a core material having formed thereover a resin coating layer.

1 8. A developer according to claim 17, wherein said resin coating layer is a copolymer containing a styrene.

19. A developer according to claim 18, wherein said copolymer is a sytrene-alkyl acrylate copolymer or a styrene-alkyl methacrylate copolymer.

20. A developer according to claim 14, wherein said toner resin is a copolymer containing a styrene.

21. A developer according to claim 20, wherein said copolymer is a styrene-alkyl acrylate copolymer or styrene-alkyl methacrylate copolymer.

22. A developer according to claim 20, wherein a toner containing said copolymer further contains a coloring agent.

23. A developer according to claim 22, wherein said coloring agent is acidic carbon black..

24. A developer according to claim 14, wherein a resin for said toner is a copolymer containing the under-defined A% by weight of a styrene and a resin forming said carrier coating layer is a copolymer containing the under-defined B% by weight of a styrene, the ratio of Said A/B satisfying the formula 0.7 < A/B < 3.0.

25. A developer according to claim 14, wherein said toner resin is a polyester resin.

26. A developer according to claim 25, wherein said polyester resin contains 5 to 25% by weight of chloroform-insolubles.

27. A developer according to claim 20, wherein said toner further contains a releasing agent.

28. A developer according to claim 27, wherein said releasing agent is a polyolefin having a softening point of 80 to 180 C, a fatty acid amide, a fatty acid or a metal salt thereof.

29. A developer according to claim 28, wherein said polyolefin is polyethylene or polypropylene.

30. A developer according to claim 18 wherein said resin is a copolymer composed of at least 3 monomer components.

31. A developer according to claim 27, wherein said copolymer is composed of at least one styrene monomer component and at least two monomer components selected from at least one of an alkyl acrylate and an alkyl methacrylate.

32. A developer according to claim 31, wherein said copolymer is composed of at least one styrene monomer component, at least one alkyl acrylate monomer component and at least one alkyl methacrylate component.

33. A toner as claimed in Claim 1 and substantially as hereinbefore described with reference to any of the Examples.

34. A developer as claimed in Claim 14 and substantially as hereinbefore described with reference to any of the Examples.