CA2147102A1 - Electrostatic image developer and image formation process using same - Google Patents
Electrostatic image developer and image formation process using sameInfo
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- CA2147102A1 CA2147102A1 CA 2147102 CA2147102A CA2147102A1 CA 2147102 A1 CA2147102 A1 CA 2147102A1 CA 2147102 CA2147102 CA 2147102 CA 2147102 A CA2147102 A CA 2147102A CA 2147102 A1 CA2147102 A1 CA 2147102A1
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- toner
- titanium oxide
- particulate
- polyolefin
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Abstract
A single-component type electrostatic image developer which provides a uniform toner chargeability distribution and causes little or no ghost and no problems concerning the toner cleanability such as adhesion to the photoreceptor, and a process for the formation of an image with the single-component type electrostatic image developer which comprises a particulate toner having a binder and a magnetic material incorporated therein and a particulate titanium oxide having an average primary particle diameter of 0.05 to 1.5 µm in an amount of 0.1 to 1.5 % by weight based on the weight of the particulate toner, the number of titanium oxide agglomerates having a grain diameter of not less than 20 µm among titanium oxide agglomerates formed by the particulate titanium oxide being 0.
Description
- - -ELECTROSTATIC IMAGE DEVELOPER AND
IMAGE FORMATION PROCESS USING SAME
FIELD OF THE INVENTION
The present invention relates to a single-component type electrostatic image developer and a process for forming an image using a single-component type electrostatic image developer.
BACKGROUND OF THE INVENTION
The dry development process for use in various electrostatic copying methods which have heretofore been put into practical use can be roughly divided into two systems, i.e., a two-component development system with a toner and a carrier such as iron powder and a single-component development system using only a toner.
Unlike the two-component development system, the single-component development system requires no automatic density adjustor and other mechanisms. Therefore, the developing machine using such a single-component development system can be compact. Further, the single-component development system is free from stain on the carrier, requiring no maintenance such as renewal of carrier. Thus, the single-component development system has been employed in low speed small-sized copying machines or printers, and nowadyas even in middle or higher speed copying machines or printers. Therefore, it has been desired to provide such a single-component development system with more improvements in -- 21~7102 properties.
Because of the nature of the single component development system (i.e., no carrier), unlike the two-component development system, the single-component type electrostatic image developer used therein tends to be insufficient in charging the praticlulate toner. As a result, the charge distribution of the particulate toner is liable to be ununiform, causing a problem of the image hysteresis of a copying cycle appearing on the subsequent cycle (ghost).
On the other hand, attempts have been made to utilize the single-component development process using a magnetic toner in easily preparing papers which can be read with a magnetic ink character reader (MICR), such as personal checks. This system is generally called an MICR system.
The MICR system is a system comprising reading a magnetized image with a magnetic head. Because the magnetic image is usually printed with a liquid magnetic ink, image formation is not easy. While a printing system using the aforesaid two-component development process has also been put to practical use, this system requires a large-sized printing machine and is still uneasy.
The magnetic toner which can be applied to an MICR
system should meet both suitability to an MICR and suitability to a printer. More specifically, the magnetic toner should provide a toner image having sufficient magnetization enough to be read with a magnetic head; the 2 ~ o 2 toner should not cause untoward problems through repeated friction with a magnetic head; the toner should be adaptable to a conventional single-component magnetic toner electrophotographic system; and the printed toner image should have image quality at least equal to that obtained in a conventional electrophotographic printing system.
In order to solve a problem of toner fall-off and magnetic head contamination with the separated toner in the MICR system, a few proposals have been made to date. For example, it has been suggested to incorporate a polyolefin into toner particles to provide a toner which can be used in a medium- to high-speed double-side copying machine, which has recently be developed for resources saving.
Incorporation of a polyolefin into toner particles aims at improvements of slip properties and anti-smudge properties of a toner image ("smudge" is a phenomenon that a fixed image is strongly scraped and thereby stained). This method proved effective to prevent smudging but still insufficient in improving scratch resistance when applied to an MICR system in which a fixed image is repeated scratched.
If a polyolefin is added in an amount higher than in a conventional toner, a further improvement of scratch resistance would be expected. However, substantially incompatible with a toner, a polyolefin added in an increased amount results in poor dispersibility, failing to obtain sufficient scratch resistance in an actual MICR system.
- -Moreover r in printing, a toner having an increased polyolefin content contaminates a toner supporting member, reduces the image density, causes background stains, and deteriorates maintenance. Furthermore, because of the poor dispersibility, it is difficult to uniformly disperse a polyolefin in the toner, resulting in lowered chargeability and non-uniform charge distribution.
In order to solve the above problems, many attempts have been proposed to uniformize the charge distribution, e.g, by adding an additive having a relatively low electrical resistance such as titanium oxide to the particulate toner.
However, additives such as titanium oxide have a high cohesiveness and thus are disadvantageous in that they adhere to the photoreceptor when used in the electrophotographic process. Thus, no single-component type electrostatic image developers satisfying the foregoing requirements have yet been available.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a single-component type electrostatic image developer which provides a uniform toner chargeability distribution and causes no ghost.
It is another object of the present invention to provide a single-component type electrostatic image developer which causes no problems concerning the toner cleanability such as adhesion to the photoreceptor.
21~7102 It is still another object of the present invention to provide a single-component type electrostatic image developer which can be suitably used in the MICR system.
It is a further object of the present invention to provide a process for forming an image using a single-component type electrostatic image developer.
These and other objects of the present invention will become more apparent from the following detailed description and examples.
The inventors made extensive studies of the foregoing problems. As a result, it was found that these objects can be accomplished by attaching a particulate titanium oxide having a predetermined particle diameter to the surface of a particulate magnetic toner in a predetermined amount and keeping the developer free of titanium oxide agglomerates having a grain diameter of not less than a predetermined value. Thus, the present invention has been worked out.
The present invention concerns a single-component type electrostatic image developer, comprising a particulate toner having a binder and a magnetic material incorporated therein and a particulate titanium oxide having an average primary particle diameter of 0.05 to 1.5 ~m in an amount of 0.1 to 1.5 % by weight based on the weight of said particulate toner, the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m among titanium oxide agglomerates formed by said particulate titanium oxide 21471~2 being 0.
The present invention also concerns a process for the formation of an image which comprises the steps of forming a latent image on a latent image carrier, and then developing said latent image with a single-component type developer which has been provided in the form of layer on a developer carrier.
DETAILED DESCRIPTION OF THE INVENTION
The single-component type electrostatic image developer of the present invention will be further described hereinafter.
The particulate toner constituting the single-component type electrostatic image developer of the present invention comprises at least a binder resin and a magnetic material.
As the magnetic material there may be any known magnetic material so far as it has heretofore been commonly used. Examples of such a known magnetic material include metal such as iron, cobalt and nickel, alloy thereof, metal oxide such as Fe3O4, y-Fe2O3 and cobalt-added iron oxide, and various ferrites such as MnZn ferrite and NiZn ferrite. These magnetic materials preferably have a particle diameter of 0.05 to 0.5 ~m.
In the present invention, the content of the magnetic material in the particulate toner is preferably from 20 to 70 % by weight, more preferably from 40 to 60 % by weight. If the content of the magnetic material falls below 20 % by weight, the chargeability of the toner may be difficult to be controlled, causing an image density drop or ununiform development particularly under a low-temperature and low-humidity atmosphere. On the contrary, if the content of the magnetic material exceeds 70 ~ by weight, the resulting toner may exhibit a reduced fixability, causing practical disadvantages.
As the binder resin there may be used a vinyl polymer. Specific examples of such a vinyl polymer include homopolymer or copolymer of one or more vinyl monomers.
Representative examples of such vinyl monomers include vinyl aromatic compounds such as styrene, p-chlorostyrene and vinylnaphthalene, halogenated vinyl compounds such as vinyl chloride, vinyl bromide and vinyl fluoride, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, vinyl formate, vinyl stearate and vinyl caproate, ethylenic monocarboxylic acids and esters thereof such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl ~-chloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate, substituted ethylenic monocarboxylic acids such as acrylonitrile, methacrylonitrile and acrylamide, ethylenic dicarboxylic acids and esters thereof such as dimethyl maleate, diethyl maleate and dibutyl -21~7102 maleate, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether and vinyl ethyl ether, vinylidene halides such as vinylidene chloride and vinylidene chlorofluoride, and N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone. Further, a resin such as polyester may be used singly or in combination with the foregoing binder resins.
The particulate toner of the present invention may further contain polyolefin to prevent smudging and to improve scratch resistance for the application to the MICR systerm.
The polyolefin is not particularly limited and may be selected from conventionally known ones, including polyolefin wax. Examples of polyolefin include polyethylene preferably having a weight average molecular weight (Mw) of from 1,500 to 16,000, more preferably from 2,000 to 6,000, and polypropylene preferably having a Mw of from 3,000 to 6,000, more preferably from 4,000 to 6,000.
The polyolefin is preferably dispersed in the particulate toner and contained in an amount of from l to 20 % by weight, particularly preferably from 2 to 15 % by weight based on the weight of the toner. The polyolefin has a mean dispersed particle diameter of from 0.01 to 0.5 ~m, preferably from 0.01 to 0.3 ~m, more preferably from 0.02 to 0.2 ~m, and most preferably from 0.03 to 0.1 ~m. If the mean 214~1Q2 . , dispersed particle diameter of the polyolefin is less than 0.01 ~m, the toner has insufficient scratch resistance in the MICR system. Polyolefin particles greater than 0.5 ~m contaminate a toner supporting member in printing for a prolonged period of time to reduce the developing properties.
The proportion of polyolefin dispersed particles of greater than 2 ~m is preferably not more than 5%, more preferably not more than 3%, and most preferably not more than 1%, based on the total number of the polyolefin particles.
The coefficient of variation of polyolefin dispersed particle size distribution is preferably from 20 to 40%, more preferably from 25 to 40%, and most preferably from 25 to 35%. If the coefficient of variation is smaller than 20%, smudges tend to become noticeable. If it is larger than 40%, development maintenance tends to be deteriorated. With the coefficient of variation falling within the above range, development maintenance is improved, and anti-fog latitude is broadened.
The coefficient of variation as above noted is measured by slicing a toner particle with a cutter, such as a microtome, to a thickness of 0.3 ~m, taking an electron micrograph at a magnification of 9,000 with a,transmission electron microscope, and analyzing about lO0 polyolefin particles randomly selected by means of an image analyzer.
The coefficient of variation (%) is obtained from formula:
(standard deviation/mean dispersed particle diameter) x 100.
-2l47lo2 -Further, the single-component type electrostatic image developer of the present invention may comprise various substances incorporated therein for the purpose of controlling the chargeability and electrical resistance thereof or like purposes. Examples of these additives include fluorinic surface active agents, dyes such as azo and salicylic metal complex, high molecular acids such as copolymer containing maleic acid as a monomeric component, quaternary ammonium salts, azine dyes such as nigrosine, and carbon black.
The particulate toner of the present invention can be prepared by any conventional process, for example, by melt-kneading a binder resin and a magnetic material with or without additives, cooling the mixture, pulverizing the cooled mixture and classifing to a desired particle size. In the case of incorporating a polyolefin into toner particles in a finely dispersed state, the polyolefin may previously be ground to powder having a particle size of not greater than 10 ~m before it is melt-kneaded with a binder resin and other toner components in a known kneading machine, such as an extruder. All the components including the polyolefin may be kneaded in the presence of water while suppressing a temperature rise so as to apply sufficient shearing force to the mixture. A dispersant, such as an oxidized wax, may be used in combination.
In the present invention, the toner is preferably 2l47lo2 produced by a process comprising previously preparing a binder resin having a polyolefin finely dispersed therein and mixing the resin with a magnetic material. According to this process, the polyolefin can be finely dispersed efficiently.
The efficiency is further increased by using a graft or block copolymer containing a polyolefin as a constituent component -(hereinafter simply referred to as a polyolefin graft or block copolymer) as a dispersant. It is preferred that the polyolefin graft or block copolymer as a dispersant comprise at least one of the monomer units constituting the binder resin. In this case, the size distribution of the polyolefin fine particles is further narrowed.
In carrying out the above-mentioned process in which a binder resin having a polyolefin finely dispersed therein is previously prepared, the polyolefin may be added to a system for preparation of a binder resin, for example, during polymerization of monomers or may be added to a binder resin in a molten state and dispersed therein in the presence of the above-mentioned polyolefin graft or block copolymer as a dispersant to a dispersed particle size of not greater than 3 ~m. A part of the polyolefin may be added to the polymerization system to form a polyolefin graft or block copolymer, which serves as a dispersant. In this case, there is obtained a binder resin containing polyolefin fine particles with a narrow particle size distribution.
Dispersion of a polyolefin to a desired particle size 214~102 is preferably effected in the following two-step process. In the first step, a polyolefin is previously dispersed in a binder resin to a particle size of not more than about 3 ~m.
The polyolefin may be dispersed in a system for producing a binder resin, for example, at the time of polymerization or in a molten binder resin by using a block or grafted polymer as a dispersing agent. More specifically, a polyolefin powder is dissolved in a solution containing a monomer for the binder resin and graft polymerization is carried out using a polymerization initiator. Alternatively, a polyolefin powder is dissolved in a solution containing a binder resin, together with a graft polymer of the monomer of the binder resin and a vinyl monomer as a dispersing agent.
While the binder resin may be a resin having two molecular weight distribution peaks corresponding to a low molecular weight component and a high molecular weight component for the sake of control of its fixing temperature, the polyolefin is preferably incorporated in a system to constitute the low molecular weight component of the binder resin in the same manner as described above.
In the second step, a commonly employed procedure for producing a toner is adopted. Prior to the second step, a solvent used in the first step is removed from the resin solution obtained in the first step. Dispersion of the polyolefin in the second step is effected simultaneously with blending and dispersing a magnetic material, etc. by means of 21~7 lO~
a roll mill, an extruder, and so on. In the second step, the polyolefin is finely dispersed to a final particle size of not more than 0.5 ~m. An additional amount of a polyolefin, either the same as or different from that added in the first step, may be added in the second step. When the above-mentioned two-molecular weight peak binder resin is used, the polyolefin to be added in the second step is preferably added to a resin solution of the first step together with a high molecular weight component of the binder resin, which is separately prepared by bulk polymerization, solution polymerization and the like. Then, the solvent of the resin solution is removed. In this case, the weight ratio of the polyolefin added in the first step to that added in the second step preferably ranges from 10:1 to 1:10 and more preferably from 1:10 to 5:10.
The coefficient of variation as defined above can be attained by the above-mentioned two-step process. The coefficient of variation can be reduced by adding the polyolefin(s) in the first and second steps in the preferred weight ratio of 1:10 to 5:10.
The thus prepared binder resin having finely dispersed therein a polyolefin is then blended with a magnetic material and melt-kneaded by means of a roll mill, an extruder or any other generally employed kneading machine.
The polyolefin particles are further reduced to 0.5 ~m or less through this kneading step. The resulting mixture is 2l~7lo~
ground and classified to obtain a toner having a desired particle size. The grinding is preferably performed by a mechanical means. The classification is preferably effected by utilizing a co-under effect.
The thus prepared particulate toner of the present invention preferably has an average particle size (D50) of from 4 to 10 ~m. The particle size of the toner is measured with a Coulter counter "TA-II" manufactured by Coulter Counter Co. at an aperture of lO0 ~m. (The term "D50" means the particle size of the particles at the time when the cumulative value of the particles reaches 50 % of the total volume of the measured particles.) As the particulate titanium oxide which serves as the other constituent component of the single-component type electrostatic image developer of the present invention there may be used a particulate titanium oxide having a specific resistivity of from 1 x 107 to 2 x 108 Q-cm. It is necessary that a particulate titanium oxide having a primary particle diameter of from 0.05 to 1.5 ~m be contained in an amount of from 0.1 to 1.5 % by weight, preferably from 0.3 to 1.2 % by weight based on the weight of the particulate toner. If the primary particle diameter and added amount of the particulate titanium oxide deviate from the above defined range, ghost cannot be inhibited.
In the present invention, the particulate titanium oxide used in the single-component type electrostatic image developer forms agglomerates thereof in the developer. It is necessary that the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m among all the titanium oxide agglomerates be 0. That is, it is necessary that substantially no titanium oxide agglomerates having a grain diameter of not less than 20 ~m be contained in the developer. If the number of such titanium oxide agglomerates is not 0, the developer is subject to adhesion to the photoreceptor, i.e., filming.
The particulate titanium oxide can be crushed during preparation so that the agglomeration thereof is reduced to keep the 500-~m mesh sieve residue at not more than 30 ~ by weight. In the present invention, a particulate titanium oxide thus obtained can be obtained. If the 500-~m mesh sieve residue exceeds 30 % by weight, the adhesion of the particulate toner to the photoreceptor can hardly be inhibited.
Further, the single-component type electrostatic image developer of the present invention may comprise a powder of other inorganic materials such as silica, powder of an organic material such as aliphatic acid, derivative thereof and metal salt thereof, powder of a resin such as fluororesin, acrylic resin and styrene resin, or the like incorporated therein in combination with the foregoing particulate titanium oxide for the purpose of improving the durability, fluidity or removability of the particulate 214~12 toner.
The process for the formation of an image with the single-component type electrostatic image developer of the present invention will be described hereinafter. The process for the formation of an image according to the present invention comprises the steps of forming a latent image on a latent image carrier, and then developing said latent image with a developer on a developer carrier. The formation of a latent image on the latent image carrier can be performed by a known method. As the latent image carrier there may be used an electrophotographic photoreceptor or dielectric. If an electrophotographic photoreceptor is used as the latent image carrier, it may be uniformly charged and then imagewise exposed to light to form an electrostatic latent image thereon.
The electrostatic latent image thus formed is then subjected to development with a developer on a developer carrier. In the present invention, the foregoing single-component type electrostatic image developer is spread over the developer carrier by means of a layer regulating member, for example, to form a thin layer thereon. The thin layer of the single-component type electrostatic image developer formed on the developer carrier is then opposed to the latent image carrier. In this manner, the particulate toner of the developer charged by the layer regulating member flies and adheres to the electrostatic latent image on the latent image -- 2l4~iQ~
-carrier to develop the electrostatic latent image.
The present invention will be further described in the following examples, but the present invention should not be construed as being limited thereto. In the Examples, all parts are by weight.
Styrene-n-butyl acrylate copolymer (copolymerization ratio: 82/12;
Mw: 150,000) 46 parts Magnetic material (magnetite having a particle diameter of 0.2 ~m) 50 parts Negatively chargeable charge controller (azo chromium compound)2 parts Polyethylene wax (Mn: 3,000) 2 parts The foregoing materials were mixed in the form of powder by means of a Henschel mixer. The mixture was then heat-kneaded for 15 minutes by means of a two-roll mill which had been adjusted to a temperature of 160 C. The mixture thus kneaded was cooled, coarsely crushed, and then finely crushed to obtain a crushed material having D50 of 8.5 ~m.
The crushed material was then classified to remove the finely divided fractions and obtain a crushed material having D50 of 9.5 ~m. To 100 parts of the crushed material were then added 0.5 part of a hydrophobic colloidal silica and 0.8 part of a particulate titanium oxide (primary particle diameter: 0.3 ~m; sieve residue (defined below): 10 % by weight). The mixture was stirred by a Henschel mixer, and then sieved 21~7102 through a 105-~m mesh sieve to remove the coarse grain fractions and obtain a developer.
A developer was prepared in the same manner as in Example 1 except that the particulate titanium oxide to be used in Example 1 was replaced by a particulate titanium oxide having the sieve residue of 50 % by weight.
A developer was prepared in the same manner as in Example 1 except that no particulate titanium oxide was used.
The developers of Example 1 and Comparative Examples 1 and 2 were then subjected to printing test with a XP-11 type printer (manufactured by Fuji Xerox Co., Ltd.) having a developing machine comprising a thin developer layer on a developer carrier under an atmosphere of 10 C and 15 % RH.
For the evaluation of ghost, the difference in the image density between the front end of a 1st solid black print produced shortly after ten sheets of continuous printing and the central part of the subsequent 2nd solid black print was determined. For the evaluation of adhesion to the photoreceptor (filming), the surface of the photoreceptor was observed after 20,000 sheets of printing. In the criterion of general evaluation, G (good) indicates good properties, F
(fair) indicates practically acceptable properties, and P
(poor) indicates practically unacceptable properties.
Table 1 Example Amount Number of Sieve Ghost Filming General No. of titanium residue (density (after evalu-titanium oxide of tit- differe- 20,000 ation oxide agglome- anium nce) sheets (wt.%) rates of (wt.%) of prin-not less ting) than 20 ~m 1 0.8 0 10 0.02 None G
Comp. 0.8 2 50 0.03 Stripe- P
Ex.1 shaped filming on image Comp. 0 0 - 0.20 None P
Ex.2 In the Table, the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m in the developer indicates the number of such titanium oxide agglomerates in a 1,000 x magnification scanning electron photomicrograph taken in a field of view. The sieve residue of the particulate titanium oxide alone is measured by the following method. 25 g of the sample is put on a 500-~m mesh sieve mounted on a shaker (Octagon 200 manufactured by Endecotts Corp.). The sample is then shaken at graduation 5 for 3 minutes. The sieve residue is then divided by the total amount of the sample to determine the percent sieve residue (by weight)(x 100).
As is apparent, the single-component type electrostatic image developer of the present invention provides a uniform chargeability distribution, making it 2~rt 10~
possible to inhibit ghost, which is a problem of the conventional magnetic toner. Further, problems concerning the cleanability of the toner such as adhesion to the photoreceptor can be solved.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
IMAGE FORMATION PROCESS USING SAME
FIELD OF THE INVENTION
The present invention relates to a single-component type electrostatic image developer and a process for forming an image using a single-component type electrostatic image developer.
BACKGROUND OF THE INVENTION
The dry development process for use in various electrostatic copying methods which have heretofore been put into practical use can be roughly divided into two systems, i.e., a two-component development system with a toner and a carrier such as iron powder and a single-component development system using only a toner.
Unlike the two-component development system, the single-component development system requires no automatic density adjustor and other mechanisms. Therefore, the developing machine using such a single-component development system can be compact. Further, the single-component development system is free from stain on the carrier, requiring no maintenance such as renewal of carrier. Thus, the single-component development system has been employed in low speed small-sized copying machines or printers, and nowadyas even in middle or higher speed copying machines or printers. Therefore, it has been desired to provide such a single-component development system with more improvements in -- 21~7102 properties.
Because of the nature of the single component development system (i.e., no carrier), unlike the two-component development system, the single-component type electrostatic image developer used therein tends to be insufficient in charging the praticlulate toner. As a result, the charge distribution of the particulate toner is liable to be ununiform, causing a problem of the image hysteresis of a copying cycle appearing on the subsequent cycle (ghost).
On the other hand, attempts have been made to utilize the single-component development process using a magnetic toner in easily preparing papers which can be read with a magnetic ink character reader (MICR), such as personal checks. This system is generally called an MICR system.
The MICR system is a system comprising reading a magnetized image with a magnetic head. Because the magnetic image is usually printed with a liquid magnetic ink, image formation is not easy. While a printing system using the aforesaid two-component development process has also been put to practical use, this system requires a large-sized printing machine and is still uneasy.
The magnetic toner which can be applied to an MICR
system should meet both suitability to an MICR and suitability to a printer. More specifically, the magnetic toner should provide a toner image having sufficient magnetization enough to be read with a magnetic head; the 2 ~ o 2 toner should not cause untoward problems through repeated friction with a magnetic head; the toner should be adaptable to a conventional single-component magnetic toner electrophotographic system; and the printed toner image should have image quality at least equal to that obtained in a conventional electrophotographic printing system.
In order to solve a problem of toner fall-off and magnetic head contamination with the separated toner in the MICR system, a few proposals have been made to date. For example, it has been suggested to incorporate a polyolefin into toner particles to provide a toner which can be used in a medium- to high-speed double-side copying machine, which has recently be developed for resources saving.
Incorporation of a polyolefin into toner particles aims at improvements of slip properties and anti-smudge properties of a toner image ("smudge" is a phenomenon that a fixed image is strongly scraped and thereby stained). This method proved effective to prevent smudging but still insufficient in improving scratch resistance when applied to an MICR system in which a fixed image is repeated scratched.
If a polyolefin is added in an amount higher than in a conventional toner, a further improvement of scratch resistance would be expected. However, substantially incompatible with a toner, a polyolefin added in an increased amount results in poor dispersibility, failing to obtain sufficient scratch resistance in an actual MICR system.
- -Moreover r in printing, a toner having an increased polyolefin content contaminates a toner supporting member, reduces the image density, causes background stains, and deteriorates maintenance. Furthermore, because of the poor dispersibility, it is difficult to uniformly disperse a polyolefin in the toner, resulting in lowered chargeability and non-uniform charge distribution.
In order to solve the above problems, many attempts have been proposed to uniformize the charge distribution, e.g, by adding an additive having a relatively low electrical resistance such as titanium oxide to the particulate toner.
However, additives such as titanium oxide have a high cohesiveness and thus are disadvantageous in that they adhere to the photoreceptor when used in the electrophotographic process. Thus, no single-component type electrostatic image developers satisfying the foregoing requirements have yet been available.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a single-component type electrostatic image developer which provides a uniform toner chargeability distribution and causes no ghost.
It is another object of the present invention to provide a single-component type electrostatic image developer which causes no problems concerning the toner cleanability such as adhesion to the photoreceptor.
21~7102 It is still another object of the present invention to provide a single-component type electrostatic image developer which can be suitably used in the MICR system.
It is a further object of the present invention to provide a process for forming an image using a single-component type electrostatic image developer.
These and other objects of the present invention will become more apparent from the following detailed description and examples.
The inventors made extensive studies of the foregoing problems. As a result, it was found that these objects can be accomplished by attaching a particulate titanium oxide having a predetermined particle diameter to the surface of a particulate magnetic toner in a predetermined amount and keeping the developer free of titanium oxide agglomerates having a grain diameter of not less than a predetermined value. Thus, the present invention has been worked out.
The present invention concerns a single-component type electrostatic image developer, comprising a particulate toner having a binder and a magnetic material incorporated therein and a particulate titanium oxide having an average primary particle diameter of 0.05 to 1.5 ~m in an amount of 0.1 to 1.5 % by weight based on the weight of said particulate toner, the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m among titanium oxide agglomerates formed by said particulate titanium oxide 21471~2 being 0.
The present invention also concerns a process for the formation of an image which comprises the steps of forming a latent image on a latent image carrier, and then developing said latent image with a single-component type developer which has been provided in the form of layer on a developer carrier.
DETAILED DESCRIPTION OF THE INVENTION
The single-component type electrostatic image developer of the present invention will be further described hereinafter.
The particulate toner constituting the single-component type electrostatic image developer of the present invention comprises at least a binder resin and a magnetic material.
As the magnetic material there may be any known magnetic material so far as it has heretofore been commonly used. Examples of such a known magnetic material include metal such as iron, cobalt and nickel, alloy thereof, metal oxide such as Fe3O4, y-Fe2O3 and cobalt-added iron oxide, and various ferrites such as MnZn ferrite and NiZn ferrite. These magnetic materials preferably have a particle diameter of 0.05 to 0.5 ~m.
In the present invention, the content of the magnetic material in the particulate toner is preferably from 20 to 70 % by weight, more preferably from 40 to 60 % by weight. If the content of the magnetic material falls below 20 % by weight, the chargeability of the toner may be difficult to be controlled, causing an image density drop or ununiform development particularly under a low-temperature and low-humidity atmosphere. On the contrary, if the content of the magnetic material exceeds 70 ~ by weight, the resulting toner may exhibit a reduced fixability, causing practical disadvantages.
As the binder resin there may be used a vinyl polymer. Specific examples of such a vinyl polymer include homopolymer or copolymer of one or more vinyl monomers.
Representative examples of such vinyl monomers include vinyl aromatic compounds such as styrene, p-chlorostyrene and vinylnaphthalene, halogenated vinyl compounds such as vinyl chloride, vinyl bromide and vinyl fluoride, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, vinyl formate, vinyl stearate and vinyl caproate, ethylenic monocarboxylic acids and esters thereof such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl ~-chloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate, substituted ethylenic monocarboxylic acids such as acrylonitrile, methacrylonitrile and acrylamide, ethylenic dicarboxylic acids and esters thereof such as dimethyl maleate, diethyl maleate and dibutyl -21~7102 maleate, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether and vinyl ethyl ether, vinylidene halides such as vinylidene chloride and vinylidene chlorofluoride, and N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone. Further, a resin such as polyester may be used singly or in combination with the foregoing binder resins.
The particulate toner of the present invention may further contain polyolefin to prevent smudging and to improve scratch resistance for the application to the MICR systerm.
The polyolefin is not particularly limited and may be selected from conventionally known ones, including polyolefin wax. Examples of polyolefin include polyethylene preferably having a weight average molecular weight (Mw) of from 1,500 to 16,000, more preferably from 2,000 to 6,000, and polypropylene preferably having a Mw of from 3,000 to 6,000, more preferably from 4,000 to 6,000.
The polyolefin is preferably dispersed in the particulate toner and contained in an amount of from l to 20 % by weight, particularly preferably from 2 to 15 % by weight based on the weight of the toner. The polyolefin has a mean dispersed particle diameter of from 0.01 to 0.5 ~m, preferably from 0.01 to 0.3 ~m, more preferably from 0.02 to 0.2 ~m, and most preferably from 0.03 to 0.1 ~m. If the mean 214~1Q2 . , dispersed particle diameter of the polyolefin is less than 0.01 ~m, the toner has insufficient scratch resistance in the MICR system. Polyolefin particles greater than 0.5 ~m contaminate a toner supporting member in printing for a prolonged period of time to reduce the developing properties.
The proportion of polyolefin dispersed particles of greater than 2 ~m is preferably not more than 5%, more preferably not more than 3%, and most preferably not more than 1%, based on the total number of the polyolefin particles.
The coefficient of variation of polyolefin dispersed particle size distribution is preferably from 20 to 40%, more preferably from 25 to 40%, and most preferably from 25 to 35%. If the coefficient of variation is smaller than 20%, smudges tend to become noticeable. If it is larger than 40%, development maintenance tends to be deteriorated. With the coefficient of variation falling within the above range, development maintenance is improved, and anti-fog latitude is broadened.
The coefficient of variation as above noted is measured by slicing a toner particle with a cutter, such as a microtome, to a thickness of 0.3 ~m, taking an electron micrograph at a magnification of 9,000 with a,transmission electron microscope, and analyzing about lO0 polyolefin particles randomly selected by means of an image analyzer.
The coefficient of variation (%) is obtained from formula:
(standard deviation/mean dispersed particle diameter) x 100.
-2l47lo2 -Further, the single-component type electrostatic image developer of the present invention may comprise various substances incorporated therein for the purpose of controlling the chargeability and electrical resistance thereof or like purposes. Examples of these additives include fluorinic surface active agents, dyes such as azo and salicylic metal complex, high molecular acids such as copolymer containing maleic acid as a monomeric component, quaternary ammonium salts, azine dyes such as nigrosine, and carbon black.
The particulate toner of the present invention can be prepared by any conventional process, for example, by melt-kneading a binder resin and a magnetic material with or without additives, cooling the mixture, pulverizing the cooled mixture and classifing to a desired particle size. In the case of incorporating a polyolefin into toner particles in a finely dispersed state, the polyolefin may previously be ground to powder having a particle size of not greater than 10 ~m before it is melt-kneaded with a binder resin and other toner components in a known kneading machine, such as an extruder. All the components including the polyolefin may be kneaded in the presence of water while suppressing a temperature rise so as to apply sufficient shearing force to the mixture. A dispersant, such as an oxidized wax, may be used in combination.
In the present invention, the toner is preferably 2l47lo2 produced by a process comprising previously preparing a binder resin having a polyolefin finely dispersed therein and mixing the resin with a magnetic material. According to this process, the polyolefin can be finely dispersed efficiently.
The efficiency is further increased by using a graft or block copolymer containing a polyolefin as a constituent component -(hereinafter simply referred to as a polyolefin graft or block copolymer) as a dispersant. It is preferred that the polyolefin graft or block copolymer as a dispersant comprise at least one of the monomer units constituting the binder resin. In this case, the size distribution of the polyolefin fine particles is further narrowed.
In carrying out the above-mentioned process in which a binder resin having a polyolefin finely dispersed therein is previously prepared, the polyolefin may be added to a system for preparation of a binder resin, for example, during polymerization of monomers or may be added to a binder resin in a molten state and dispersed therein in the presence of the above-mentioned polyolefin graft or block copolymer as a dispersant to a dispersed particle size of not greater than 3 ~m. A part of the polyolefin may be added to the polymerization system to form a polyolefin graft or block copolymer, which serves as a dispersant. In this case, there is obtained a binder resin containing polyolefin fine particles with a narrow particle size distribution.
Dispersion of a polyolefin to a desired particle size 214~102 is preferably effected in the following two-step process. In the first step, a polyolefin is previously dispersed in a binder resin to a particle size of not more than about 3 ~m.
The polyolefin may be dispersed in a system for producing a binder resin, for example, at the time of polymerization or in a molten binder resin by using a block or grafted polymer as a dispersing agent. More specifically, a polyolefin powder is dissolved in a solution containing a monomer for the binder resin and graft polymerization is carried out using a polymerization initiator. Alternatively, a polyolefin powder is dissolved in a solution containing a binder resin, together with a graft polymer of the monomer of the binder resin and a vinyl monomer as a dispersing agent.
While the binder resin may be a resin having two molecular weight distribution peaks corresponding to a low molecular weight component and a high molecular weight component for the sake of control of its fixing temperature, the polyolefin is preferably incorporated in a system to constitute the low molecular weight component of the binder resin in the same manner as described above.
In the second step, a commonly employed procedure for producing a toner is adopted. Prior to the second step, a solvent used in the first step is removed from the resin solution obtained in the first step. Dispersion of the polyolefin in the second step is effected simultaneously with blending and dispersing a magnetic material, etc. by means of 21~7 lO~
a roll mill, an extruder, and so on. In the second step, the polyolefin is finely dispersed to a final particle size of not more than 0.5 ~m. An additional amount of a polyolefin, either the same as or different from that added in the first step, may be added in the second step. When the above-mentioned two-molecular weight peak binder resin is used, the polyolefin to be added in the second step is preferably added to a resin solution of the first step together with a high molecular weight component of the binder resin, which is separately prepared by bulk polymerization, solution polymerization and the like. Then, the solvent of the resin solution is removed. In this case, the weight ratio of the polyolefin added in the first step to that added in the second step preferably ranges from 10:1 to 1:10 and more preferably from 1:10 to 5:10.
The coefficient of variation as defined above can be attained by the above-mentioned two-step process. The coefficient of variation can be reduced by adding the polyolefin(s) in the first and second steps in the preferred weight ratio of 1:10 to 5:10.
The thus prepared binder resin having finely dispersed therein a polyolefin is then blended with a magnetic material and melt-kneaded by means of a roll mill, an extruder or any other generally employed kneading machine.
The polyolefin particles are further reduced to 0.5 ~m or less through this kneading step. The resulting mixture is 2l~7lo~
ground and classified to obtain a toner having a desired particle size. The grinding is preferably performed by a mechanical means. The classification is preferably effected by utilizing a co-under effect.
The thus prepared particulate toner of the present invention preferably has an average particle size (D50) of from 4 to 10 ~m. The particle size of the toner is measured with a Coulter counter "TA-II" manufactured by Coulter Counter Co. at an aperture of lO0 ~m. (The term "D50" means the particle size of the particles at the time when the cumulative value of the particles reaches 50 % of the total volume of the measured particles.) As the particulate titanium oxide which serves as the other constituent component of the single-component type electrostatic image developer of the present invention there may be used a particulate titanium oxide having a specific resistivity of from 1 x 107 to 2 x 108 Q-cm. It is necessary that a particulate titanium oxide having a primary particle diameter of from 0.05 to 1.5 ~m be contained in an amount of from 0.1 to 1.5 % by weight, preferably from 0.3 to 1.2 % by weight based on the weight of the particulate toner. If the primary particle diameter and added amount of the particulate titanium oxide deviate from the above defined range, ghost cannot be inhibited.
In the present invention, the particulate titanium oxide used in the single-component type electrostatic image developer forms agglomerates thereof in the developer. It is necessary that the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m among all the titanium oxide agglomerates be 0. That is, it is necessary that substantially no titanium oxide agglomerates having a grain diameter of not less than 20 ~m be contained in the developer. If the number of such titanium oxide agglomerates is not 0, the developer is subject to adhesion to the photoreceptor, i.e., filming.
The particulate titanium oxide can be crushed during preparation so that the agglomeration thereof is reduced to keep the 500-~m mesh sieve residue at not more than 30 ~ by weight. In the present invention, a particulate titanium oxide thus obtained can be obtained. If the 500-~m mesh sieve residue exceeds 30 % by weight, the adhesion of the particulate toner to the photoreceptor can hardly be inhibited.
Further, the single-component type electrostatic image developer of the present invention may comprise a powder of other inorganic materials such as silica, powder of an organic material such as aliphatic acid, derivative thereof and metal salt thereof, powder of a resin such as fluororesin, acrylic resin and styrene resin, or the like incorporated therein in combination with the foregoing particulate titanium oxide for the purpose of improving the durability, fluidity or removability of the particulate 214~12 toner.
The process for the formation of an image with the single-component type electrostatic image developer of the present invention will be described hereinafter. The process for the formation of an image according to the present invention comprises the steps of forming a latent image on a latent image carrier, and then developing said latent image with a developer on a developer carrier. The formation of a latent image on the latent image carrier can be performed by a known method. As the latent image carrier there may be used an electrophotographic photoreceptor or dielectric. If an electrophotographic photoreceptor is used as the latent image carrier, it may be uniformly charged and then imagewise exposed to light to form an electrostatic latent image thereon.
The electrostatic latent image thus formed is then subjected to development with a developer on a developer carrier. In the present invention, the foregoing single-component type electrostatic image developer is spread over the developer carrier by means of a layer regulating member, for example, to form a thin layer thereon. The thin layer of the single-component type electrostatic image developer formed on the developer carrier is then opposed to the latent image carrier. In this manner, the particulate toner of the developer charged by the layer regulating member flies and adheres to the electrostatic latent image on the latent image -- 2l4~iQ~
-carrier to develop the electrostatic latent image.
The present invention will be further described in the following examples, but the present invention should not be construed as being limited thereto. In the Examples, all parts are by weight.
Styrene-n-butyl acrylate copolymer (copolymerization ratio: 82/12;
Mw: 150,000) 46 parts Magnetic material (magnetite having a particle diameter of 0.2 ~m) 50 parts Negatively chargeable charge controller (azo chromium compound)2 parts Polyethylene wax (Mn: 3,000) 2 parts The foregoing materials were mixed in the form of powder by means of a Henschel mixer. The mixture was then heat-kneaded for 15 minutes by means of a two-roll mill which had been adjusted to a temperature of 160 C. The mixture thus kneaded was cooled, coarsely crushed, and then finely crushed to obtain a crushed material having D50 of 8.5 ~m.
The crushed material was then classified to remove the finely divided fractions and obtain a crushed material having D50 of 9.5 ~m. To 100 parts of the crushed material were then added 0.5 part of a hydrophobic colloidal silica and 0.8 part of a particulate titanium oxide (primary particle diameter: 0.3 ~m; sieve residue (defined below): 10 % by weight). The mixture was stirred by a Henschel mixer, and then sieved 21~7102 through a 105-~m mesh sieve to remove the coarse grain fractions and obtain a developer.
A developer was prepared in the same manner as in Example 1 except that the particulate titanium oxide to be used in Example 1 was replaced by a particulate titanium oxide having the sieve residue of 50 % by weight.
A developer was prepared in the same manner as in Example 1 except that no particulate titanium oxide was used.
The developers of Example 1 and Comparative Examples 1 and 2 were then subjected to printing test with a XP-11 type printer (manufactured by Fuji Xerox Co., Ltd.) having a developing machine comprising a thin developer layer on a developer carrier under an atmosphere of 10 C and 15 % RH.
For the evaluation of ghost, the difference in the image density between the front end of a 1st solid black print produced shortly after ten sheets of continuous printing and the central part of the subsequent 2nd solid black print was determined. For the evaluation of adhesion to the photoreceptor (filming), the surface of the photoreceptor was observed after 20,000 sheets of printing. In the criterion of general evaluation, G (good) indicates good properties, F
(fair) indicates practically acceptable properties, and P
(poor) indicates practically unacceptable properties.
Table 1 Example Amount Number of Sieve Ghost Filming General No. of titanium residue (density (after evalu-titanium oxide of tit- differe- 20,000 ation oxide agglome- anium nce) sheets (wt.%) rates of (wt.%) of prin-not less ting) than 20 ~m 1 0.8 0 10 0.02 None G
Comp. 0.8 2 50 0.03 Stripe- P
Ex.1 shaped filming on image Comp. 0 0 - 0.20 None P
Ex.2 In the Table, the number of titanium oxide agglomerates having a grain diameter of not less than 20 ~m in the developer indicates the number of such titanium oxide agglomerates in a 1,000 x magnification scanning electron photomicrograph taken in a field of view. The sieve residue of the particulate titanium oxide alone is measured by the following method. 25 g of the sample is put on a 500-~m mesh sieve mounted on a shaker (Octagon 200 manufactured by Endecotts Corp.). The sample is then shaken at graduation 5 for 3 minutes. The sieve residue is then divided by the total amount of the sample to determine the percent sieve residue (by weight)(x 100).
As is apparent, the single-component type electrostatic image developer of the present invention provides a uniform chargeability distribution, making it 2~rt 10~
possible to inhibit ghost, which is a problem of the conventional magnetic toner. Further, problems concerning the cleanability of the toner such as adhesion to the photoreceptor can be solved.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Claims (9)
1. A single-component type electrostatic image developer, comprising a particulate toner having a binder and a magnetic material incorporated therein and a particulate titanium oxide having an average primary particle diameter of 0.05 to 1.5 µm in an amount of 0.1 to 1.5 % by weight based on the weight of said particulate toner, the number of titanium oxide agglomerates having a grain diameter of not less than 20 µm among titanium oxide agglomerates formed by said particulate titanium oxide being 0.
2. The single-component type electrostatic image developer according to Claim 1, wherein the amount of said magnetic material is from 20 to 70 % by weight based on the weight of said particulate toner.
3. The single-component type electrostatic image developer according to Claim 1, wherein said particulate titanium oxide has a 500-µm mesh sieve residue of not more than 30 % by weight.
4. The single-component type electrostatic image developer according to Claim 1, wherein said particulate titanium oxide is crushed.
5. The single-component type electrostatic image developer according to Claim 1, wherein said particulate toner contains polyolefin dispersed therein in an amount of from 1 to 20 % by weight based on the weight of the toner.
6. The single-component type electrostatic image developer according to Claim 5, wherein said dispersed polyolefin has a mean dispersed particle diameter of from 0.01 to 0.5 µm.
7. The single-component type electrostatic image developer according to Claim 5, wherein said polyolefin is polyethylene or polypropylene.
8. The single-component type electrostatic image developer according to Claim 5, wherein said polyolefin has a coefficient of variation of dispersed particle diameter of from 20 to 40%.
9. A process for the formation of an image which comprises the steps of forming a latent image on a latent image carrier, and then developing said latent image with a developer which has been provided on a developer carrier in the form of layer, said developer being a single-component type electrostatic image developer as defined in Claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6167535A JPH0815898A (en) | 1994-06-28 | 1994-06-28 | Electrostatic charge image developer and image forming method |
| JP6-167535 | 1994-06-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2147102A1 true CA2147102A1 (en) | 1995-12-29 |
Family
ID=15851503
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2147102 Abandoned CA2147102A1 (en) | 1994-06-28 | 1995-04-13 | Electrostatic image developer and image formation process using same |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH0815898A (en) |
| CA (1) | CA2147102A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3595631B2 (en) * | 1996-07-31 | 2004-12-02 | キヤノン株式会社 | Toner for developing electrostatic images |
| JP4401452B2 (en) * | 1998-07-31 | 2010-01-20 | キヤノン株式会社 | Image forming method and image forming toner |
| JP4602880B2 (en) * | 2004-09-17 | 2010-12-22 | 株式会社リコー | Toner, developer, toner container, process cartridge, image forming apparatus, and image forming method |
-
1994
- 1994-06-28 JP JP6167535A patent/JPH0815898A/en active Pending
-
1995
- 1995-04-13 CA CA 2147102 patent/CA2147102A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0815898A (en) | 1996-01-19 |
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