JPH02207275A - Carrier for electrophotography - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier for electrophotography, and more particularly to a carrier useful for full-color copying.

[Prior Art] Electrophotography uses a corona discharge to apply a negative electrostatic charge to a photoconductive layer, and then exposes the photoconductive layer to a light image corresponding to the original, thereby eliminating the charge in the exposed area and forming a latent image. Do this.

Development is carried out by depositing toner on the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image depending on the amount of charge on the photoconductive layer, forming a toner image with shading. This toner image is transferred to the support surface and permanently fixed to the support surface using a suitable fixing means such as heat, pressure, solvent treatment, or overcoating.

Many developing methods are known. Examples include a cascade development method, a magnetic brush method, and a touchdown method.

In addition, the so-called J/ There is a B development method.

A typical method is the magnetic brush method. That is, magnetic particles such as copper or ferrite are used as carriers, and a developer consisting of toner and magnetic carrier is held by a magnet, and the magnetic field of the magnet arranges the developer in a brush shape.

When this magnetic brush contacts the electrostatic latent image surface on the photoconductive layer, only toner is attracted from the brush to the electrostatic latent image to effect development.

In this developing method, the compositions of both toner and carrier are as follows:
Mutual contact friction is such that the toner is chosen to have a polarity opposite to that of the photoconductive layer. Further, as a result of the contact friction between the two, the carrier electrostatically adheres the toner to the surface, and as a developer, the carrier transports the toner within the developing device and supplies the toner onto the photoconductive layer.

Generally, when a two-component developer is used to continuously copy a large number of sheets using an electronic copying device, images with clear and good image quality can be obtained initially, but after tens of thousands of sheets have been copied, the edge effect with a lot of fog becomes noticeable. The result is an image with poor continuous gradation and clarity.

Particularly in color copying using chromatic colors, continuous gradation is an important factor that affects image quality.

In other words, after copying a large number of copies, the occurrence of an edge effect in which only the periphery of the image is emphasized greatly impairs the gradation of the image.
A pseudo contour is formed near the actual contour due to the edge effect, which impairs copy reproducibility including color reproducibility in color copying. In addition, in the case of color copying, the original used in conventional black-and-white copying has an image area of 10% or less, and the images are mostly line images, such as letters, literature, and reports. ,
The image area is at least 20% or more, and solid images with gradation, such as photographs, catalogs, maps, and paintings, occupy a considerable area.

When continuous copying is performed using such an original with a large image area, copies with high image density are normally obtained at the beginning, but
The density may gradually decrease, or the replenishment toner and carrier may be mixed in an insufficiently charged state, causing fog, or there may be a partial toner density (indicating the mixing ratio of toner and carrier) on the developing sleeve. ) increases and decreases, resulting in image blurring and uniformity of image white density.

This is because the amount of toner contained in the developer, that is, the toner concentration, is too low, or because the frictional charging between the supplied toner and the carrier in the developer does not quickly rise, resulting in uncontrolled and insufficiently charged toner. By being involved in development, etc.
It is thought that insufficient development and fogging occur. As a developer for color copying, it is essential to have the ability to always output high-quality images even when continuously copying originals with large image areas. Conventionally, in order to cope with such documents having a large image area and a very large amount of toner consumption, it has been necessary to improve the developing device rather than improving the developer itself. That is,
In order to increase the chance of contact with the electrostatic latent image on the developing sleeve,
Efforts have been made to increase the circumferential speed of the developing sleeve and to increase the size of the developing sleeve to a larger diameter.

Although these measures improve the developing capacity, they cause contamination inside the machine due to toner scattering due to centrifugal force from the developing device, and overload on the developing device drive unit, which significantly limits the device life.

Furthermore, in order to compensate for the lack of developing capacity of the developer, a large amount of developer may be put into the developing device, but this also increases the weight of the developing device and overloads the drive unit. Moreover, this is not very preferable since it results in an increase in cost due to an increase in the size of the device.

Until now, there has been no developer that satisfies the characteristics unique to color copying, which makes it possible to continuously copy images with a large image area with a small amount of developer, and which does not cause edge effects even after durability.

Indeed, many studies have been conducted regarding developers and carriers, and many inventions have been disclosed. However, most of these were invented with black-and-white copying in mind, and very few inventions have particular features for full-color copying. In addition, it has the ability to continue copying images with an image area of 20% or more that is close to the sunset image, reduces edge effects, and maintains uniformity of image density among copies. A career with the ability has not yet been found.

[Problems to be Solved by the Invention] An object of the present invention is to provide an electrophotographic carrier that does not cause a decrease in image density or cause blurring even when a color original with a large image area is continuously copied.

Another object of the present invention is to provide an electrophotographic carrier capable of producing color copies with little edge effect even after repeated duplication.

Another object of the present invention is to provide a carrier for electrophotography in which frictional charging between toner and carrier can quickly rise.

Another object is to provide an electrophotographic carrier in which triboelectric charging is less dependent on the environment.

Another object of the present invention is to provide an electrophotographic carrier that can be easily transported within a developing device.

[Means and effects for solving the problems] The present invention is characterized in that the average particle size and the particle size of particles accounting for 80% or more of the total weight of the carrier are in the range of 65 to 40 gm, and
The purpose is to use an electrophotographic carrier made of ferrite containing more than one metal.

Inventions that suggest the average particle diameter and particle size distribution of carriers, such as the present invention, are disclosed in JP-A-51-3238 and JP-A-58-
It is described in JP-A No. 144839, JP-A No. 61-204846, etc. Japanese Patent Application Laid-Open No. 51-3238 is
Although the rough particle size distribution is mentioned, the magnetic properties, which are closely related to the developability of the developer and the transportability within the developing device, are not mentioned at all. Furthermore, all the carriers in the examples in the publication were 250 mesh (approximately 80 gm).
The above is about 80% by weight or more, which is far beyond the scope of the present invention, and the average particle size is 60p or more. I can't help but think that there is.

Moreover, JP-A-58-144839 only specifies the average particle size, and as in the present invention, the carrier has a much sharper particle size distribution than conventional carriers, and is suitable for use on photoreceptors. It does not take into account the reduction of carrier adhesion or image quality reproducibility in color copying.

Furthermore, Japanese Patent Application Laid-Open No. 81-2041 (48) and the like only focus on the combination of a copying device and a suitable developer, and do not discuss the particle size distribution or magnetic properties of the carrier proposed in the present invention. Furthermore, the above-mentioned publication does not even disclose why the developer is effective for the copying apparatus.

Additionally, the present applicant and others have filed applications based on the magnetic force of carriers, such as in Japanese Patent Laid-Open No. 49-70830, but these applications involve iron powder, which has a higher specific gravity than ferrite, as a carrier material. The saturation magnetism is also higher than that of the present invention.

Further, the ferrite carrier disclosed in JP-A No. 58-23032 is a porous material with many pores, and according to the studies of the present inventors, edge effects do not occur in such carriers. It has been found that it is not suitable as a carrier for color copying because it is easily damaged by cracks, chips, etc. due to shocks and collisions in the developing device due to repeated copying, and has poor durability.

In Japanese Patent Application Laid-Open No. 83-418Eta, 10 to 651
It is stated that 80% or more of the particles are contained in the range of L. However, according to the present inventors' study of a developing method based on the magnetic brush method, ferrite carriers with a diameter of about 20 mm, which is approximately twice the toner particle size, are likely to be accompanied by the toner during development; It has been found that carrier adhesion to the photoreceptor is likely to occur.

This means that the theoretical maximum σS (saturation magnetization) of currently commonly used ferrite carriers is at most 80 to 90.
emu/g, and the value of σS is expressed as an amount per unit gr. That is, as the particle size of the carrier becomes smaller, the weight per carrier inevitably decreases, and as the particle size becomes smaller, the σS of the carrier decreases. In the magnetic brush method, this σS indicates the force with which the carrier stays on the developing sleeve, that is, the holding force, and as σS decreases, this holding force also decreases. According to experiments conducted by the present inventors, ferrite carriers having particle diameters around 20 IL or less inevitably have a small σS and a relatively small holding force on the sleeve. As a result, the reliability of the photoreceptor 2 has been dramatically increased.

The carrier for electrophotography of the present invention has a very sharply defined particle size distribution with 80% of the total number of particles falling within the range of 11 of only 25 μl, which has an adverse effect on chargeability with toner and carrier adhesion. There are almost no fine powder carriers of 20 to 301 or less and coarse powder carriers of 65 μm or more, which exert a negative effect. For this reason, the rise in triboelectricity with the toner is also favorably improved. In addition, since the carrier is small in particle size and homogeneous, the amount of toner with good chargeability that can be mixed with the carrier is much larger than in a carrier with a broad particle size. This exhibits a more preferable effect than when using a toner having an average particle size of 5 to 10, which has a smaller particle size.

When a carrier with a broad particle size is used, it is difficult to obtain sufficient charge for the toner mixed with the fine powder carrier, and the fine powder carrier often accompanies the toner during development, causing carrier adhesion on the photoreceptor. cause it to occur. Further, the toner mixed with the coarse powder carrier often acquires too high an amount of charge during charging, resulting in a toner that is difficult to develop.

The average particle diameter of the carrier of the present invention is preferably 40 to 65 μm, more preferably 45 to 60 μm. If the average particle size is less than 40 l, the image density will decrease due to toner charge-up and carrier adhesion to the photoreceptor will increase, and if the average particle size is more than 65 l, fine line reproducibility in color copying will deteriorate.

In addition, the weight of particles in the range of 65 to 40 ILI11 must be 80% or more of the total weight, preferably 85%.
It is more preferably 80% or more. If it is less than 80%, it becomes difficult to obtain uniform charging with the toner.

Further, the magnetic properties of the carrier greatly affect the development properties and transportability of the developer. Particularly in color copying, as mentioned above, image uniformity and gradation are important.

If the saturation magnetization is 80 emu/g or more (for an applied magnetic field of 3000 oersted), a brush-like accumulation composed of carrier and toner will also occur on the developing sleeve facing the electrostatic latent image on the developing surface photoreceptor. The image becomes hard and compact, and the reproduction of gradation and intermediate tones deteriorates. Also 50em
If it is less than u/g, it becomes difficult to hold the toner and carrier on the developing sleeve, resulting in a disadvantage that fogging and toner scattering become worse. Furthermore, if the residual magnetization and coercive force of the carrier are too high, this will hinder the good conveyance of the developer in the developing device, making image defects such as blurring and uneven density in solid images more likely to occur, reducing the developing ability. Become something. Therefore, in order to maintain developability in color copying, unlike general black and white copying, the residual magnetization and coercive force should preferably be 10 emu/g or less and 1008 or less (for 3000 oersted applied magnetic field), respectively, 5 emu/g.
Below, 8. It is important that it is OOe or less.

Examples of the toner binder resin used with the carrier of the present invention include polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, and styrene-butadiene copolymer. styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-
Ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer,
Styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methacrylate copolymer) acid phenyl copolymer, etc.), styrene-
Styrenic resins such as α-methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (styrene or a styrene-substituted homopolymer or copolymer), vinyl chloride resin, styrene-vinyl acetate Copolymer rosin modified maleic acid resin, phenol resin, epoxy resin, polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl Butyral resin etc. can be used. Particularly preferred resins for carrying out the present invention include styrene-acrylic acid ester resins and polyester resins.

In particular, the following formula (wherein R is ethylene or propylene group, a'l, X,
Each y is an integer of 1 or more, and the average value of X+y is 2 to 10. ) as a diol component, and a carboxylic acid component consisting of a divalent or higher carboxylic acid, its acid anhydride, or its lower alkyl ester, such as fumaric acid, maleic acid, maleic anhydride, phthalate. A polyester resin obtained by cocondensation polymerization with at least an acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc. is particularly preferable because it has sharp melting characteristics.

As the carrier used in the present invention, known materials can be used as long as they do not interfere with the gist of the present invention, such as surface oxidized or unoxidized iron, nickel, copper, zinc, cobalt, manganese, chromium, rare earth. , alloys or oxides thereof, and ferrites. Particularly preferably, ferrites containing two or more metals selected from zinc, copper, nickel, and cobalt can be used. Moreover, there are no special restrictions on the manufacturing method.

It is also possible to coat the surface of the carrier with a resin or the like. As a method for this, any conventionally known method can be applied, such as a method in which a coating material such as a resin is dissolved or suspended in a solvent and applied and adhered to the carrier, or a method in which a powder is simply mixed.

Substances that adhere to the carrier surface vary depending on the toner material, but include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of ditertiary butylsalicylic acid, styrene resin, and acrylic. It is appropriate to use one or more of these resins, polyacid, polyvinyl butyral, nigrosine, aminoacrylate resin, basic dye and its lake, fine silica powder, fine alumina powder, etc., but the invention is not necessarily limited thereto.

The amount of the compound mentioned above may be appropriately determined so that the carrier satisfies the above conditions, but generally the total amount is 0.1 to 30% by weight (preferably 0.5% by weight) based on the carrier of the present invention.
~20% by weight) is desirable.

In the present invention, as a particularly preferred embodiment, Gu-Z
It is a ternary ferrite of n-Fe, and its surface is made of a combination of resins such as fluorine resin and styrene resin, such as polyvinylidene fluoride and styrene methyl methacrylate resin: polytetrafluoroethylene and styrene methyl methacrylate resin. , a fluorine-based copolymer and a styrene-based copolymer; etc. in a ratio of 90:10 to 20:80, preferably 70:30 to 30% by weight, preferably 0.01 to 5% by weight. is 0.1-1% by weight
Examples include coated ferrite carriers. As the fluorine-based copolymer, vinylidene fluoride/lafluoroethylene copolymer (lO: 8
Examples of styrenic copolymers include styrene-acrylic #, 2-ethylhexyl (20:10 to 90:10).
:80-80:20), styrene-2-ethylhexyne acrylate-methyl methacrylate (20-60:5-3
0:10-50) is exemplified.

Or, as a particularly more preferred embodiment, a coated ferrite coated with 0.1 to 10% by weight of a mixture of a 5-component copolymer of styrene methyl methacrylate, butyl acrylate, 2 ethylhexyl methacrylate, and methacrylic acid, and a fluorine copolymer. Career is an example.

When preparing a two-component developer by mixing with color toner,
Good results are usually obtained when the mixing ratio is 3.0% to 15% by weight, preferably 4.0% to 13% by weight, in terms of toner concentration in the developer. Toner density is 3
．． If it is less than 0%, the image density is too low to be practical, and 1
If it exceeds 5%, fogging and in-machine scattering increase, and the useful life of the developer tends to be shortened.

Among the colorants used together with the carrier of the present invention to form a color developer, dyes include, for example, C
,1, Direct Red 1, C,1, Direct Red 4, C,1, Acid Red 1. C.I.

Basic Red 1, C, 1, Modern Red 30,
G.1. Direct Blue 1, G, 1. There are Direct Blue 2, C,1, Acid Blue 9, C,1, Acid Blue 15, C,1, Basic Blue 3, C,1, Basic Blue 5, C,1, Mordand Blue, etc.

Pigments include Naphthol Yellow S, Hansa Yellow G, Permanent Yellow NCG, Permanent Orange GTR, Hirazolone Orange, Benzidine Orange G, Permanent Red 4R, Wounching Red Calcium Salt, Brilliant Carmine 3B, First Violet B, Methyl Violet Lake, There are phthalocyanine blues, first sky blue, indanthremblu-BC, etc.

Preferably, the pigments are disazo yellow, insoluble azo, and copper phthalocyanine, and the dyes are basic dyes and oil-soluble dyes.

Particularly preferably G, 1. pigment yellow 17, C,
1, Pigment Yellow 15, G, 1. Pigment Yellow 13, C, 1, Pigment Yellow 14, C, 1,
Pigment Yellow 12, G, 1. Big Men Trend 5
,G.I.

Pigment Red 3, G, 1. Pigment Red 2C,
1, Pigment Red 6, C, 1, Pigment Red 7
,G,1. Pigment Blue 15, C,1, Pigment Blue 16 or having the structural formula (1) shown below,
copper phthalocyanine pigments, etc.

(Hereinafter, blank space) n=1 to 4 As dyes, G, 1. Solvent Red 49, G, 1.
Solvent Red 52, C, 1, Solvent Red 10
9, C,1, Paysic Red 12, C,1, Paysic Red 1, c,r, Paysic Red 3b, etc.

The method for measuring particle size distribution in the present invention is as follows.

1. Weigh 100g of the sample to the nearest 0.1g.

2. For the sieve, use a standard sieve of 100Mesh to 400Mesh (hereinafter referred to as sieve), and 100.145.
Stack them in the order of size 200, 250, 350, and 400, place a tray at the bottom, put the sample in a sieve, and cover with a lid.

3. This is sifted for 15 minutes using a vibrator at a horizontal rotation rate of 285±6 times per minute and an impulse rate of 150±10 times per minute. Weigh it to the nearest 1g.

5. Calculate the weight percentage to the second decimal place, JIS284
Round to the first decimal place by 01.

(However, the dimensions of the sieve frame are such that the inner diameter above the sieve surface is 200 m.
The depth from the top surface of m to the sieve surface is 45 mm, and the total weight of the iron powder in each part is 99 mm of the starting mass of the sample.
% or less. ) Also, the average particle diameter is determined from the above-mentioned particle size distribution measurement values according to the following formula.

140 + (remaining amount of 145MESH sieve) x 122
+ (remaining amount of 200 MESH sieve) x so+ (2
50MESH sieve remaining amount)
38+(Total sieve passing amount) x 17) A BHU-EIO magnetic type lateralization measuring device (manufactured by Kenkei) is used as a measuring device for the magnetic properties of the carrier. The measurement sample is approximately 1.
Weigh out 0g, pack it into a cell with an inner diameter of 7rnrnφ and a height of 10mm, and set it in the above-mentioned apparatus.

The measurement is carried out by gradually increasing the applied magnetic field up to a maximum of 3000 oersteds. Then, the applied magnetic field is reduced and finally a hysteresis curve of the sample is obtained on the recording paper. From this, calculate saturation magnetization, residual magnetization, and coercive force.

[Example] The present invention will be described in detail below with reference to Examples.

Example 1 To 100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, the coloring agent and charge control agent in the prescribed amounts shown in Table 1 were used to produce yellow, yellow and charge control agents, respectively.
Magenta, cyan, and black color toners were obtained.

The manufacturing method is to sufficiently premix the above prescribed amounts using a Henschel mixer, melt-knead at least twice using a three-roll mill, cool, and then coarsely grind to about 1 to 2 mm using a hammer mill. It was pulverized to a particle size of 40 gm or less using an air jet type pulverizer. The obtained finely ground product was further classified, and silica fine powder was selected to have the particle size distribution of the present invention, with a volume average diameter of 8.2 JL, and treated with hexamethyldisilazane as a fluidity improver. To 100 parts by weight of each classified product, 0.7 part by weight was added as an external additive to prepare a color toner.

3 to 10 parts by weight of these color toners were mixed with carrier (2) shown in Table 2 in a total amount of 100 parts by weight to prepare a developer. This carrier (■) contains PVDFPTFE copolymer (copolymerization weight ratio 8:2) and St-2EHAMMA copolymer (copolymerization weight ratio 45:20:35), ■=
It is a coated ferrite carrier coated with a film thickness of about 0.5 μl at a weight ratio of 1:1.

The developer concentrations of yellow, magenta, cyan, and black color toners are 5% and 5%, respectively.

It was set to 6% and 5%.

A copying test was conducted using a color electrophotographic apparatus having an OPC photosensitive drum shown in FIGS. 1 and 2.

Development and transfer of each color toner was performed in the order of magenta toner, cyan toner, yellow toner, and black toner. The developer is passed through the developer regulating blade 14 on the developing sleeve 13.
This results in a constant amount of developer, and the negatively charged toner is transferred to the photosensitive drum 2 by a reversal development method at the opposing portion of the photosensitive drum 1 having the negatively charged electrostatic latent image.

Using this method and using an original with an image area of about 40% in full color mode, a full color image that faithfully reproduces the original color chart with little edge effect was obtained even after printing 30,000 sheets. Furthermore, images without blurring or density reduction were obtained even during continuous copying, and transport within the copying machine and developer concentration detection were also good and stable. Even when an OHP film was used, desirable uniformity and good adhesion of the toner to the solid area was obtained, and the permeability was very favorable.

Example 2 Coloring agents for magenta were C, R, and PASIC RED 1°0.
8 parts by weight and c, r, disperse violet 31,
A monochrome magenta toner durability test was conducted using Carrier (1) in Table 2 with the amount changed to 0.2 parts by weight, and even after 2,000,000 copies, good image density and clear images were obtained.

Example 3 Using carrier O in Table 2, cyan colorants C and I were used.

Same as Example 1 except that 6.0 parts of Pigment Blue 15 (α type), 2.3 parts of yellow colorant C,1, and Disperse Yellow 54 were used, and an original with an image area of 50% was used. Using the same method, under a high temperature and high humidity environment (32.5°C)
285% RH), images with good color balance and no fog were obtained.

Example 4 Using carrier 0 in Table 2, yellow colorants were C, 1,
Pigment Yellow 17 was changed to 4.6 parts by weight, and a yellow monochrome durability test was conducted in the same manner as in Example 1, but performance without problems in conveyance and developer mixing properties was obtained even during continuous copying. Ta.

Comparative Example 1 Example 2 except for changing the carrier to carrier ■ in Table 2
A test was conducted in the same manner as above, but during continuous copying, the image density gradually decreased, and the appearance of gradation 1 with sharp edges became poor.

Also, during durability, toner may become spent on the carrier.
Due to the decrease in triboelectric charging ability, the particles were seriously scattered inside the machine after 80,000 sheets, contaminating the developer detection fibers and making detection impossible.

Under high temperature and high humidity conditions, the frictional charge between the toner and the toner decreases significantly, and the magenta image density is extremely high, exceeding 2.0 according to a Macbeth reflectance meter, and there is a lot of fog caused by toner adhesion to non-image areas, which is not practical. It seemed impossible.

(The following is a margin) [Effects of the Invention] The present invention has a sharply limited particle size distribution and is composed of ferrite containing two or more metals, so it is possible to continuously copy color originals with a large image area. However, color copies with no reduction in image density or blurring can be obtained even when the color copy is used, the environmental dependence of triboelectric charging is small, and the transportability within the developing device is good.

[Brief explanation of the drawing]

FIGS. 1 and 2 show the O used in the embodiment of the present invention.
FIG. 1 is an explanatory diagram of a color electrophotographic apparatus having a PC photosensitive drum.

Claims (2)

[Claims] (1) An electrophotographic carrier made of ferrite having an average particle size and a particle size of 80% or more of the total weight of the carrier in the range of 65 to 40 μm, and containing two or more metals. (2) The carrier for electrophotography according to claim 1, wherein the ferrite has a saturation magnetization of 50 to 80 emu/g, and a residual magnetization and a coercive force of 10 emu/g or less and 10 ■e or less, respectively.