JPH02163758A - Carrier for electrophotography - Google Patents

Abstract

PURPOSE:To improve water resistance, toner spent property and electrostatic chargeability by subjecting a core material contg. an acrylic resin consisting of a ferrite core material having a specific surface area and average grain size to a coating treatment with >=2wt.% resin. CONSTITUTION:The ferrite core material having the specific surface area S and average grain size (d) expressed by equation I and equation II is coated with the resin at >=2wt.% of the weight of the core material contg. the acrylic resin. The relation between the image quality and the carrier sticking is made into an adequate range and the fine ruggedness is increased in the surface of the core material when the surface area S and average grain size (d) are specified to the value expressed by formula I and formula II. The surface coating resin is impregnated into the bottom of the fine ruggedness, and has good adhesiveness to the core material. The acrylic resin has good adhesiveness to ferrite and allows sufficient coating on the surface ruggedness. The water resistance, toner spent property and the electrostatic chargeability are improved in such a manner.

Description

[Detailed Description of the Invention] [Industrial Application Field] 7 (The invention relates to a carrier used in a 4-densha Page River developer,
In particular, it relates to a ferrite carrier whose surface is coated with resin.

[Prior art] Electrophotography is a method in which electrostatic charges are generated on the surface of a photoreceptor having a photoconductive layer by means such as corona discharge, and a light image corresponding to the original is irradiated onto the charged photoconductive layer. By doing this, an electrostatic latent image is formed, and then colored fine powder called toner having the opposite polarity is deposited on the electrostatic latent image to form the electrostatic latent image. After developing the image and transferring the toner image to a transfer material such as paper as necessary, it is fixed by heat, pressure, solvent vapor, etc. to obtain a copy.

Methods of developing using toner can be broadly divided into methods using a so-called two-component developer in which toner is dispersed in a medium called a carrier.

There is a method using a so-called two-component developer that uses toner alone without using a carrier. The carriers constituting the two-component developer are broadly classified into conductive carriers and insulating carriers. A typical insulating carrier is one in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite is uniformly coated with an insulating resin, but for electrophotography, bias, In order to prevent U pressure from leaking, a ferrite core material with a certain degree of high resistance is suitable. In a developer using this carrier, toner particles are less likely to be fused to the carrier surface than in the case of a conductive carrier, and at the same time, the J9! It has the advantage that it is easy to control triboelectric properties, has excellent durability, and has a long service life, making it particularly suitable for high-speed electronic copying machines. However, in this insulating carrier, the coating layer covering the surface of the carrier core material has sufficient repulsion resistance and strong adhesion with the core material (durability);
The coating layer must have good adhesion prevention properties to prevent toner from forming a film on the carrier surface (toner spent properties), and J? It is required that a desired charging state of size and polarity can be obtained by rubbing (charging property).

That is, the carrier is rubbed against other carrier particles or toner particles in the developing device, but when the toner adheres to the surface of the carrier object and forms a film, the charging characteristics become unstable.

Conventionally, a coated carrier coated with a fluorine-containing resin has been proposed as a technique to solve this drawback (U.S. Pat. No. 3,922,382). A carrier coated only with basic polymer is! In order to improve the film-forming properties of fluorine-containing polymers, we use polymers with relatively good film-forming properties. A carrier coated with a mixture of carriers has also been proposed (U.S. Pat. No. 4,297,427, Japanese Unexamined Patent Publication No. 110839/1983). This results in deterioration of toner spent characteristics and chargeability.

[Problems to be Solved by the Invention] As stated above, the purpose of the present invention is to solve the four conventional problems of resin-coated carriers: durability, toner spendability, and chargeability. The objective is to provide a resin-coated ferrite carrier that solves the problem.

[! Means and operation for solving the problem 2I] As a result of extensive research to solve the above problems, the present inventor has found that the surface properties of the ferrite core material improve the durability of the carrier after resin coating, and the durability of the toner spent. It was found that there is a close relationship between the electrostatic properties and the electrostatic properties. That is, the surface properties of the core material are related to its adhesion to the coating resin and influence its Jlil impact.

Roughly speaking, specific surface area is generally used as a parameter expressing surface properties, but specific surface area is also a parameter for particle size, and particle size has an optimum range in relation to image quality and carrier adhesion. , specific surface area S (cm
'/g), when the average particle size is d (continuous layer), 30≦
d≦200 (Il) and S×d≧2.0 (c layer 37
In the case of using a ferrite core material in the range g), a resin-coated carrier having fewer of the above-mentioned drawbacks can be obtained. That is, in the case of core materials having the same particle size, a large specific surface area means that there are many fine irregularities on the surface. Also.

As the particle size becomes smaller, the specific surface area increases even if the surface properties are the same, so the surface properties cannot be expressed only by the value of the specific surface area.

When the surface of the core material has many fine irregularities, the resin coated on the surface penetrates into the valleys of the fine irregularities, resulting in extremely good adhesion to the core material and improved durability.

However, since the surface has minute irregularities, the amount of coating resin needs to be larger than before, and the coating resin must also contain at least an acrylic resin that has extremely good adhesion to ferrite. It becomes necessary.

The particle size of the carrier is effectively in the range of 30 μm to 20,014 g, preferably 40 μm to 150 μm. 30
Below the μm layer, adhesion to the photosensitive drum begins to occur, causing problems such as damage to the drum and bias leakage when bias is applied. Further, if the layer is 200 μm or more, a high quality image cannot be obtained.

On the other hand, when S Average.

In addition, as the acrylic resin to be coated, general single ones or several types of copolymers are used, and the monomers include, for example, styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, p- Styrene derivatives such as chlorostyrene, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, hebutyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate.

undecyl methacrylate, dodecyl methacrylate, glycidyl methacrylate, methoxyethyl methacrylate, propoxyethyl methacrylate, butoxyethyl methacrylate, acrylic ugly methyl ethyl acrylate, acrylic ugly propyl, acrylic ugly butyl, pentyl acrylate, hexyl acrylate, There are heptyl acrylates, octyl acrylates, nonyl acrylates, decyl acrylates, undecyl acrylates, and dodecyl acrylates, but those containing hydroxyl groups are particularly good for adhesion to ferrite core materials. It is effective to copolymerize an acrylic resin, and it is especially effective when used in combination with a non-acrylic resin such as a fluoropolymer.As an acrylic resin monomer containing a hydroxyl group, 2-hydroxyl acrylate, 2-hydroxyl acrylate
Hydroxypropyl, hydroxybutyl acrylate, 2-hydroxy-3-phenyloxypropyl acrylate, methacryl @ 2-hydroxyethyl, methacryl ugly 2
-hydroxypropyl, hydroxybutyl methacrylate, 2-hydroxy-3-phenyloxypropyl methacrylate, and the like. These monomers are used so that the hydroxyl value of the copolymer is 1-10100 (KOH/g). Preferably 5-TO (KOHmg/g)
, more preferably 10 to 50 (KOHig/g). If this value is small, the binding property with the carrier core material will be insufficient, and the coating will be easily destroyed by impact, friction, etc.

On the other hand, if it is too large, hygroscopicity increases and charging stability under high temperature and high humidity conditions is lost.

Furthermore, as mentioned above, since the surface 1h of the carrier is relatively large, the amount of resin coated must be greater than conventionally, and is 2 wt% or more based on the core material.

Preferably, 3 to 10 wt% is appropriate. If the amount is less than 2 wt%, the surface of the carrier core material cannot be uniformly covered with the resin, and stable performance as a carrier cannot be expected.

The specific surface precision value 5 cta'/g used here is determined as follows.

[Measuring device] Shimajiru powder specific surface area measuring device (SS-100 model) [Measuring method] ■ Place a sieve plate in a plastic sample tube, place a piece of filter paper on the top of the sieve plate, and place the sample on the top of the tube so that it covers 1/2 of the sample tube. Enter up to 3.

(ri) Set the sample tube on the tap stand of the powder tester and tap for 1 minute.

(i) Add the sample to the tapped sample tube up to 273 of the sample tube.

(4) Note L (Perform the same operation as @.

(Insert a supplementary tube (plastic) on top of one tube of 0 sample, and place the sample in a heap from above.

(Φ　Perform the same operation as ① above.

■ ■ ■ Ch p ff1 Remove the supplementary tube from the tapped sample tube and cut off the excess sample with a spatula.

Fill the specific surface measurement tube with water up to the S scale.

Connect the sample cylinder to the measuring tube.

(After filling the sample, apply grease to the grating surface.

Open the cock at the bottom outlet and start the stopwatch when the water level in the measuring tube passes the 0 scale.

(Catch the water flowing from the bottom in a beaker.) Measure the time for the water level to drop to the 20 scale (unit: cc).

Remove the sample tube and measure the weight of the sample.

Calculate the specific surface S using the formula below.

S = Specific surface area of powder (cm2/g) Text = Porosity of sample packed bed ρ = Density of grain powder (R/cm3) η = Viscosity coefficient of fluid (g/c "5ec) L = = Porosity of the material bed Thickness (C dew) Q = Sample layer permeation flow rate ec) t = Time required for Qcc fluid (air) to permeate the sample layer (sec) ΔP = Pressure difference between both ends of the sample layer Cg/cta2) A ==Cross-sectional area of the material layer (c+17) W=Weight of the sample (g) In the present invention, the ferrite particles are specifically made of a complete mixture of a suitable metal oxide and iron oxide.
Ni, Zn, Nn, Mg, C:u, Li, Ha
It is a sintered body of oxides of , Va, and Ga'p and trivalent iron oxide.

The manufacturing method for this ferrite core material is - sterilization;
For example, Fe20x and metal oxides such as GuO, ZnO, etc. are blended in a desired ratio, and then ground and mixed in a wet ball mill or the like for more than 1 hour. The slurry thus obtained is dried and smoked, and after being ground, it is heated to 700°C or more. Calculate at 1200℃. Thereafter, further milling is performed using a wet ball mill etc. to a diameter of 5 μm or less, preferably 2 μm.
After pulverizing to 4 or less, it is granulated and maintained at 1000°C to 1600°C for 1 to 12 hours.

This baked product is crushed and classified! Arrange.

Adjustment of the specific surface area and particle size of the core material can be achieved by adjusting the pulverization, granulation stage, firing temperature/time, etc. during the above-mentioned steps.

This will be explained below using Example F.

[Example] Example 1 Fe20x = 60 mol%, ZnO = 25 mol%,
CuO=15 mol % was ground and mixed in a wet ball mill for 12 hours, dried, and then calcined at 900° C. for 4 hours.

This was further pulverized for 24 hours in a wet ball mill to obtain an average particle size of 32.Q ha or more.
P, V, A-1, Owt$), average particle size 70g
The pellets were granulated to a size of about m.

Next, this granulated powder was fired at 1000°C for 6 hours, and then crushed and classified for 1 time to obtain ferrite powder with an average particle size of 72 gm.
), the specific surface area of this ferrite powder is 420C'/g
(S X d = 3.02 cm3/g)
.

This ferrite core material is 100%! Acrylic resin (styrene-methyl methacrylate-2-hydroxyethyl methacrylate copolymer) and fluororesin (vinylidene fluoride and tetrafluoroethylene copolymer) were each added in a solid content of 2. Ofl'<9 parts were cooled and coated in a solvent. The coating carrier is WurS
It was obtained by spray coating in a ter-type circulating fluidization bed, followed by a drying process. This carrier is A1
shall be.

The resin-coated carrier A1 thus obtained and red toner for NP4835 manufactured by Canon were mixed at a main stem ratio of 9228 to obtain a developer.

This developer was applied to a 1fP4835 color developer.

When NP4835 was used for 100,000 sheets, it showed good performance as shown in Table 1-1.

Further, when this carrier was separated from the toner and its surface was examined using a microscope, it was found that it had a smooth resin-coated surface with almost no significant difference between before and after !M. In addition, when these carriers were mixed with a new toner (toner concentration: 8 $) and the tripod charge was measured, the initial charge was +16.2 gc/g, and after 100,000 sheets of printing = +14.8 JLc/g. It was shown that there was very little toner spent and peeling of the coating layer.

(Left below) Approx. 1 unit using the same raw materials as in Example 1. Granulated powder of Og, m was obtained.

This granulated powder was fired at 1600°C for 8 hours and then pulverized and classified into 1 class to obtain ferrite powder with an average particle size of 70p and m. The specific surface area of this ferrite powder was 205c+2/g (S x d = 1.435 cm3/g).

For this ferrite core material, 11t of the same tree as in Example 1 was used.
Neat carrier B was obtained by coating t in the same manner.
I got 1. Using this B1, NP48 was prepared in the same manner as in Example 1.
When the 100,000-sheet image printing durability test was carried out with No. 35, as shown in Table 1, there were no problems in initial performance, but as the durability progressed, fogging, hissing, etc. increased slightly. Furthermore, when this carrier was separated from the toner and observed under an electron microscope, no particular abnormality was observed in the initial state, but after 10,000 sheets of durability, many parts of the carrier core material were exposed on the sides. It was done. When these carriers were mixed with a new toner and the tripocharge amount was measured, it was initially = +15 pc/g, but after running for 100,000 sheets, it decreased to = +IO,2 gc/g.

YoJl or FerO: + = 80 mol%, Zn0 = 10 mol%,
Cu0 = 4 mol% and Ni0 = 6 mol% were ground and mixed in a wet ball mill for 12 hours, dried and then heated to 900°C 4)
It was calcined for 1r. This is further ground in a wet ball mill,
The average particle size was set to 21° or more.

This sample was granulated using a binder (P, V, A=1.0wt1) so that the average particle size was about 100μ.

Next, this granulated powder was fired at 1100° C. for 6 hours, then crushed and classified to obtain ferrite powder with an average particle size of 00 μm. The specific surface area of this ferrite powder was 270 cm2/g (S x d = 2.7 cmJ/g).

A coating solution was prepared by diluting 5 parts by weight of an acrylic resin (combined styrene-methyl methacrylate) in a solvent with respect to 100 parts by weight of this ferrite core material, and the coating solution was prepared in the same manner as in Example 1. Coating carrier A2
I got it.

A developer was prepared using this A2 carrier and a toner for Canon's NP5000 (toner density: 2 wt$), and the amount of tripo charge was measured, and it was found to be -7.4 p, c/g.

When this developer was used to print 100,000 images on NP5000, the results were extremely good as shown in Table 1.
Separate the carrier from the developer after printing.

When mixed with the new toner (toner concentration 2%), the amount of triboelectric charge was measured in the same manner as above, and it was found to be -7.1pc/
g, there was almost no change from the initial state, and it became clear that there was no deterioration of the carrier.

Further, when the surface of the carrier after 100,000 sheets was subjected to surface i11* analysis using an electron microscope, it remained smooth with almost no signs of peeling of the coating.

[Effects of the Invention] As described above, according to the present invention, even after printing 100,000 or more images, there is no deterioration such as fogging or hist and the same quality as the initial quality can be guaranteed.

Applicant: Kinyan Co., Ltd. Agent C 1) Kei Yu

Claims (1)

[Claims] Where S is the specific surface area and d is the average particle size, 30≦d≦200 (μm) and S×d≧2.0 (cm
A carrier for electrophotography, characterized in that a ferrite core material of ^3/g) is coated with a resin containing at least acrylic resin, the amount of which is 2 wt% or more based on the core material.