JPH02264268A - Carrier for electrophotography - Google Patents

Abstract

PURPOSE:To decrease the spent state of a toner by coating the carrier with a resin dispersed with a graphite specified in grain size and a conductive carbon black. CONSTITUTION:The carrier is coated with the resin dispersed with the graphite powder having 0.1 to 5.0mum grain size and the carbon black powder sized <=0.1mum. The carbon black connects the graphite and the graphite or the graphite and a core material to form microconductive paths and, therefore, the sufficient durability and wear resistance are imparted to the coating layer while the surface resistance is lowered by a relatively small amt. of the mixed system composed of the graphite and the carbon black. The spent state of the toner is prevented in this way and the images having the good quality are obtd. over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier that constitutes an electrostatic image developer together with a toner.

[Prior art] As an electrophotographic method, US Pat.
Various methods are described in Publication No. 4748, etc., but in all of these methods, an electrostatic latent image is formed by irradiating a photoconductive layer with a light image corresponding to the document, and then the electrostatic latent image is The electrostatic latent image is developed by attaching colored fine powder called toner having the opposite polarity onto the image, and if necessary, after transferring the toner image to a transfer material such as paper, heat or pressure is applied. Alternatively, copies can be obtained by fixing with solvent vapor or the like.

The process of developing the electrostatic latent image involves attracting toner particles charged with a polarity opposite to that of the latent image by electrostatic attraction and depositing them on the static ttU image. There are two main methods for developing with toner: two-component developers in which a small amount of toner is dispersed in a medium called a carrier, and one-component developers in which toner is used alone without using a carrier. There is a method to use.

Generally, carriers constituting such two-component developers are broadly classified into conductive carriers and insulating carriers.

Oxidized or unoxidized iron powder is usually used as a conductive carrier, but in a developer containing this iron powder carrier, the triboelectricity of the toner is unstable, and the toner is formed by the developer. It has the disadvantage that capri occurs in the visible image. In other words, as the developer is used, toner particles adhere to the surface of the iron powder carrier particles, which increases the electrical resistance of the carrier particles, lowers the bias current, and makes triboelectric charging unstable, resulting in the formation of toner particles. The image density of the visible image decreases and fog increases.

In addition, even in conventional developers using insulating carriers, some of the toner particles are attached to the surface of the carrier particles due to collisions between particles, mechanical collisions such as collisions between particles and developing machines, or heat generated by these. It has the property of physically adhering to form a film, that is, becoming spent. When this happens, a film of toner material gradually accumulates on the surface of the carrier particles, and the frictional charge between the carrier particles and toner particles is replaced by the frictional charge between the toner particles, causing the overall friction of the developer to increase. The charging characteristics deteriorate, and as a result, a so-called background smudge phenomenon occurs in which a large amount of toner adheres to the background portion of the copied image, resulting in a decrease in copy quality. Furthermore, if a toner film is formed on the surface of the carrier, the entire developer must be replaced, which is a drawback that increases costs.

In order to prevent such spent formation, methods of coating the surface of the carrier with various resins have been proposed, but none have been able to provide a satisfactory -F component.

For example, a carrier coated with a fluororesin such as tetrafluoroethylene copolymer has a low critical surface tension, so it is difficult for the toner to become spent, but it has poor film-forming properties and cannot cover the carrier core material sufficiently uniformly. Therefore, stable charging characteristics cannot be obtained. Furthermore, the adhesion to the core material is weak and the abrasion resistance is unsatisfactory.

Furthermore, due to its relationship with the charging series, fluororesin-coated carriers cannot have sufficient charging ability for negatively charging toner.

On the other hand, carriers coated with acrylic resins such as styrene/methacrylate copolymers have good film-forming properties, strong adhesion to the carrier core material, and excellent abrasion resistance, making them comparable to the aforementioned fluorine-based resins. Used in combination or alone. However, since this acrylic resin has a relatively high critical surface tension, toner is likely to be spent when used repeatedly, causing some problems in the lifespan of the developer. Furthermore, due to its good film-forming properties, the carrier tends to have a high resistance, and as a result, toner tends to be difficult to separate from the carrier due to toner charge-up.

Furthermore, if development is continued for a long time in a state in which the toner is difficult to separate from the carrier, the above-mentioned spending of the carrier by the toner is further accelerated, which is undesirable.

In addition, if the resistance of the carrier is too high, the image density may decrease, the reproducibility of solid halftones may deteriorate, or the carrier may be developed onto the photoreceptor, causing damage to the photoreceptor, or the carrier may adhere to the image. Sometimes it happens.

In order to solve these problems, attempts have been made to control the resistance by dispersing conductive fine particles in a carrier coat resin. For example, Tokuko Sho 53-8
No. 535 discloses the addition of conductive fine particles of 0.1 μm or less, and JP-A-54-73 also discloses
A number of issues such as Publication No. 43 are being considered. However, there is still room for improvement in these proposed methods.
Adding a necessary and sufficient amount of conductive fine powder to lower resistance results in 1. 2. The adhesion between the core material and the resin decreases. The problem is that the triboelectric charging ability decreases (especially under high humidity).

[Problems to be Solved by the Invention] In view of the current problems as described above, an object of the present invention is to solve the following points.

A first object of the present invention is to provide a resin-coated carrier that causes less spent toner.

A second object of the present invention is to provide a resin-coated carrier that is difficult to charge up.

A third object of the present invention is to provide a resin-coated carrier that has stable charging characteristics even when used repeatedly.

A fourth object of the present invention is to provide a resin-coated carrier with excellent abrasion resistance.

[Means and Actions for Solving the Problems] In order to achieve the above-mentioned objects, the present invention provides a method in which graphite powder with a particle size of 0.1 to 5.0 μm and carbon black powder with a particle size of 0.1 μm or less are dispersed. The present invention provides a carrier characterized by being coated with a resin.

The reason why graphite is used in the present invention is that graphite has the following properties: ■ It is scaly, ■ It has excellent lubricity, and ■ It has high conductivity. That's why.

In other words, since the scale-like graphite is on the surface, its slipperiness makes it difficult for toner to stick to it, and even if it sticks (
Even if it is made into a spent material, it is easily peeled off due to its highly cleavable scale shape, so new surfaces are always likely to appear. In addition, it is thought that this is because, due to its conductivity, charge accumulates on the surface of the carrier, promoting the separation of the toner from the carrier.

However, there is still room for improvement for the purpose of lowering the surface resistance of coated carriers. That is,
Graphite itself is a highly conductive substance, but
The particle size is relatively large, and Ko! In order to sufficiently lower the resistance as an agent, graphite alone requires the addition of a considerable amount. However, addition of a large amount of graphite reduces the adhesion of the resin to the core material, making it unsuitable as a carrier coating agent. This is true not only for graphite, but also for conductive carbon black with extremely small particle sizes.Furthermore, the addition of a large amount of carbon black tends to reduce its ability to triboelectrically charge the toner. This is especially noticeable under high humidity.

The purpose of the present invention is to have relatively large particle sizes (,
Among the properties of ■, graphite especially has ■, ■,
This was achieved for the first time by using a mixed system of conductive carbon black with an extremely small particle size to bring out the properties of graphite (1) even when added in small quantities.

A conceptual diagram of the present invention is shown in FIG. The reason why carbon black has sufficient durability and abrasion resistance as a coating layer while reducing surface resistance with a relatively small amount of mixture of graphite and carbon black is that carbon black connects graphite and graphite or graphite and core material. We believe that this is because they form microscopic conductive paths.

In addition, the larger the particle size of the graphite used, the more pronounced the above properties ① and ③, and the greater the effect of the present invention.
On the contrary, it becomes difficult to uniformly disperse it into the coating resin, making it unsuitable as an additive to the coating resin. For this reason, the particle size of graphite needs to be 0.IILm or more and 5.0μm or less, and is preferably 0.IILm or more, although it depends on the amount added.
IILm~3. It's OH.

In addition, since it has excellent lubricity, the graphite used must have a particle shape with a friction coefficient of 0.3 or less. Furthermore, in order to desire the above-mentioned high conductivity, graphite having a specific electrical resistance of 2 Ω·cm or less, preferably 1 Ω·cm or less is preferable.

On the other hand, the particle size of the carbon black used is 0.1Ω.
It is necessary that it is less than m. Also, high conductivity m, +r
Therefore, like graphite, carbon black with a specific electrical resistance of 2 Ω·cm or less, preferably 1 Ω·cm or less is preferable.

The mixing ratio of graphite and carbon black is such that the ratio of graphite is 99 to 10% by weight, preferably 97 to 3% by weight.
0% by weight, more preferably 95-50% by weight. 9
If the content is 9% by weight or more, the effects based on the above-mentioned graphite properties (1) and (2) can be sufficiently obtained, but the resistance as a carrier coating material is not sufficiently lowered. On the other hand, if it is less than 10% by weight, the effects based on the properties (1) and (2) peculiar to graphite cannot be obtained.

On the other hand, the amount of graphite and carbon black mixed powder added to the coat resin is 0.1 to 30% by weight, preferably 0.5 to 20% by weight, based on the resin. If it is less than 0.1% by weight, the effect of the present invention will not be significant, and if it is more than 30% by weight, the durability and abrasion resistance of the coating film, which are one of the characteristics of the present invention, will not be sufficient.

As the resin to which the graphite and carbon black mixed powder is added, resins that are generally used as carrier coating resins can be used. For example, natural resins, polyolefin resins/polyvinyl, polyvinylidene resins, fluorocarbon resins, polyamide resins, polyester resins,
These include polyurethane resins, polycarbonate resins, phenol resins, acrylic resins, melamine resins, amino resins, epoxy resins, and mixtures thereof.

As the carrier core material used in the present invention, general materials such as iron powder and ferrite are used, and the particle size thereof is 10 to 10.
A suitable thickness is 1000 μm, preferably 20 to 200 μm.

The coating amount of the coating material according to the present invention is such that the solid content of the coating material is 0.1 to 20% by weight (preferably 0.5 to 10% by weight) based on the carrier core material. If it is less than 0.1% by weight, the effect of the coating will be insufficient, and if it exceeds 20% by weight, the effect of the graphite and carbon black mixed powder of the present invention will be insufficient.

In order to coat the surface of the carrier core material with the resin to which the above-mentioned mixed powder of graphite and carbon black is added, the resin is dissolved or suspended in a solvent, and then the graphite powder and carbon black powder are added. Powders mixed at a predetermined ratio are added, sufficiently dispersed with a disperser, and applied by a general method such as spraying.

[Examples] Example 1 A coating liquid having the following formulation was prepared and coated on a carrier core material to obtain a coated carrier.

(The following is a blank space) Coating liquid carrier The above coating liquid was prepared by mixing 1 and 0.0 at a predetermined ratio and dispersing the mixture in a ball mill pot for 24 hours. Further, the carrier core material was coated by a spray method using a fluidized bed.

This carrier and Canon equipped full color copier CLC-
1 magenta toner at a temperature/humidity of N/ji(2
J”C/60%), II/I+(32,5°C/8
5%) and L/L (15°C/10%) at a toner concentration of 8% to prepare a developer. The amount of charge of this developer was as shown in Table-1. Using this developer, N/N, I+ in one CLC knee
/+1. When images were produced using the actual machine in each of L/L environments, high-definition images with sufficient density were obtained.

Furthermore, the above developer was put into the CLC-1 developing device, and an external idle rotator that rotates only the sleeve without image formation was used to carry out idle rotation durability for 4 hours in an L/L environment. Charge-up and carrier deterioration in L were simulated for durability. When an image was produced using the CLC-1 using the developer containing the developer after this idle rotation endurance test, a high-density, high-definition image with a density of 1.3 or higher, which was almost the same as the initial image, was obtained, and the charge at L/L was It was found that the toner spent on the carrier was not deteriorated. Furthermore, only the carrier was separated from the developer after this L/L idle rotation durability, mixed with new toner again, and the charge m was measured. As shown in Table 1, it was almost the same as before the durability. It showed a value of 0. This also indicates that there is no deterioration in durability due to toner spent or the like on the carrier.

Comparative Example 1 A coated carrier was obtained in the same manner as in Example 1, except that in the formulation of the coating liquid in Example 1, graphite (■) and carbon black (O) were removed, and only ■ was used. When evaluated in the same manner as in Example 1, the image after L/L idle rotation durability (:LC-1) had a density of 0.95.
It was getting low. Furthermore, the amount of charge caused by the carrier after separation was -10.51 pc/g, which was lower than the initial value of about 172, indicating that some carrier deterioration had occurred.

Comparative Example 2 A coated carrier was obtained in the same manner as in Example 1 except that only O graphite was removed from the coating liquid formulation in Example 1.

As shown in Table 1, its performance is almost the same as Comparative Example 1, and the idling durability results are also almost the same as Comparative Example 1, indicating that the effect of adding only carbon black is insufficient. Understood.

Comparative Example 3 A carrier was produced in the same manner as in Comparative Example 2 except that the amount of carbon black added was changed to 10% by weight based on the resin solid content. Using this carrier, we performed the same evaluation as in Example 1, and as shown in Table 1, the amount of charge of the developer decreased under high temperature and high humidity conditions, and even when producing images on actual equipment at +1/H. , some fogging was noticeable, and after 5,000 sheets of durability, scattering into the inside of the machine became noticeable.

Example 2 A coated carrier was obtained in the same manner as in Example 1 using the recipe shown below.

Coating liquid carrier This carrier and red toner for NP4g35 manufactured by Canon were mixed at a toner concentration of 8% to obtain a developer. The developer thus prepared was evaluated in the same manner as in Example 1, except that NP4835 was used for the developing device and copying machine.

As a result, N/N, II/H, L/L of NP4835
In each of the images under each environment, high-definition images with a density of 1.2 or higher and no fogging or blurring were obtained. Also, N
The image after 4 hours of L/L idle rotation endurance using P4835 developing device was also good, and the charge amount of a new developer prepared by separating only the carrier from the developer after this endurance is shown in Table 1. As shown, there was almost no difference from the initial value.

Comparative Example 4 A coated carrier was obtained in the same manner as in Example 2, except that the graphite (■) and the carbon black (O) were removed and only (■) was used. When the same evaluation as in Example 2 was conducted using this carrier, L
/L The image of NP4g35 after idle rotation endurance has a density of 0.
It was as low as 85.

Further, the amount of charge of the new developer due to the carrier after separation was also reduced to about 273, which is the amount of charge due to the new carrier, indicating that carrier deterioration had occurred.

Comparative Example 5 In the formulation of the coating liquid in Example 2, only the graphite (■) was removed, and only the carbon black (O) was added to 5 parts (0/Φ = 57
A carrier was prepared in the same manner using a carrier having a weight ratio of 100%.

Using this carrier, a developer was prepared in the same manner as in Example 2, and the amount of charge was measured: +2.8 #Lc/g
There was no L. When the surface of this carrier was observed using an electron microscope, it was found that the coating material was not uniformly coated and a considerable portion of the core material was exposed.

Comparative Example 6 Carrier core material in Example 2 (spherical ferrite, 72
pm), a developer similar to Example 2 was prepared using an uncoated carrier, and the amount of charge in each environment was measured. As shown in Table 1, only low values were obtained. Ta.

Table 1 (blank below) Example 3 Coating liquid carrier A coated carrier was obtained in the same manner as in Example 1 using the above formulation.

When this carrier and toner for Canon NP-5500 were mixed to prepare a developer (toner concentration: 2%), the amount of charge was -7.8 pc/g. When images were produced on 20,000 copies using NP-5500 using this developer, good images as good as the initial images were obtained. After this durability, the carrier was separated and mixed with new toner, and the amount of charge was measured, which was -7.51 Lc/g, which was almost the same as the initial value.

Comparative Example 7 In Example 3, a carrier was prepared with ■ and O removed, and the same evaluation was performed. The charge amount of the agent was -5.8 μc/g/-8.1 pc/g, and a decrease due to durability was observed.

[Effects of the Invention] As explained above, the carrier of the present invention can prevent toner from becoming spent, and can provide high-quality images for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the present invention.

Claims (1)

[Claims] An electrophotographic carrier characterized in that the carrier is coated with a resin in which graphite having a particle size of 0.1 to 5.0 μm and conductive carbon black having a particle size of 0.1 μm or less are dispersed.