DE3140639A1 - Electrophotographic process - Google Patents

Abstract

In an electrophotographic process with magnetic brush development, a developer is used which has particles with high specific resistance and particles with low specific resistance. The specific electrical resistance of the developer can be changed to correspond with the strength of the electric field applied for development and picture transfer. If the developer which remains on a photoconductor carrying a latent electrostatic image is recovered after picture transfer and is reused, a developer is refilled which has the same mixing ratio of particles having a high and a low specific resistance as the mixing ratio of the developer transferred to a sheet of photocopy paper, whereas if the developer which remains on the photoconducting drum after a development is removed, without being recycled, a developer is refilled which has the same mixing ratio of particles having a high and a low specific resistance as the mixing ratio of the developer applied to the photoconductor. <IMAGE>

Description

_ £ "" 3U0639

l attorney's file; 31 848

description

,. The invention relates to an electrophotographic process according to the preamble of claim 1.

Conventional electrophotographic processes can be of two types according to the types of developers used

_{lfi can be classified} by methods, namely, a wet method in which liquid developers are used and a dry method in which powder developers are used. Although both types of electrophotographic processes have certain advantages and disadvantages in certain cases,

In general, the dry process becomes the wet process preferred, and consequently a variety of implementations are made of the dry electrophotographic process studied and created for practice.

2Q For example, a dry electrophotographic method is disclosed in Japanese Patent Application Laid-Open S.N. 4 9-4523 / 1974 described in which a magnetic one-component toner with a specific volume or diameter

11

contact resistance of 10 jfi cm or less is used.

25 This process creates an electrostatic charge pattern generated in the form of a latent, electrostatic image on the surface of a photoconductor, and this electrostatic Charge pattern induces electrical charges of a polarity similar to that of the electrostatic charge pattern

30 on the surface layer of each toner particle on a developing sleeve is opposite. Due to the electrical forces created by those in the surface layer of the toner particles induced electrical charges have been generated, the toner particles are attached to the latent, electrostatic

35's image is attracted so that it develops on the photoconductor will.

* This electrophotographic process contains toner a relatively low, specific volume resistance is used, and as a result, electric charges are generated on the surface layer of the toner particles in is induced in the development in an extremely short time, and accordingly the development efficiency is quite high. In this method, however, the transfer or copy sheet on which the developed image is from the surface of the photoconductor can be treated so that it is electrically isolated. Otherwise electrical will flow The toner particles are easily charged across the paper and the developing efficiency becomes lower and consequently the quality of the developed images will deteriorate significantly. This occurs in particular when

* 5 uncoated paper with a relatively low specific electrical volume resistance is used. On the other hand, when the aforementioned type of toner is used, must a corresponding recording sheet, for example a sheet coated with zinc oxide, can be used. At the-

^{In this} process, an electrostatic latent image is formed directly on the recording sheet and is developed directly on the recording sheet omitting the image transfer step.

In order to overcome the drawbacks of the aforementioned conventional methods, a method has been proposed in which a toner with a high specific throughput

1 3

resistance of 10 jLcm or more is used. With this one Due to the high specific throughput

resistance of the toner, the image transfer efficiency can be increased, and hence the above-mentioned Disadvantages that occur at the time of an image transfer, be eliminated. However, due to the high volume resistivity of the toner for

a development of insufficient electrostatic charges

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on the surface layer of the developed on the developing sleeve Toner particles are induced, and consequently the latent, electrostatic image on the surface of the The photoconductor cannot be developed with a high degree of sharpness, so that the development efficiency is then lowered is.

This poor development efficiency can be improved to some extent by interposing the gap the surface of the photoconductor and the development sleeve is reduced significantly, or that additional electrical Charges are applied to the toner particles during the development step. When reducing the Gap between the surface of the photoconductor and the developing sleeve, it is extremely difficult to mechanically the maintain a narrow gap with high accuracy, so that this method is impractical. Also in the process Applying additional electrical charges to the toner particles is uniform charge application extremely difficult and therefore not particularly practical either.

According to the invention, therefore, an electrophotographic Methods can be created with which high quality images are obtained, using uncoated paper as an image transfer s sheet and a developer are used, which is a mixture of particles with a high specific electrical volume resistance of more than 10 j £ 2.cm and particles with a low volume resistivity of not more than 10 Λ cm, preferably of

less than 10Jd cm, with the development of latent electrostatic images on a photoconductive one Material by applying the developer, which is attracted in the form of a brush to a developing sleeve with internal magnets has been carried out on the latent, electrostatic images and then an image transfer of the

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wrapped images of the photoconductive material onto uncoated Paper is made.

In the electrophotographic process according to the invention, the particles with a low specificity serve Volume resistance as an electrostatic induction promoting agent and the developer from that described above Mixture behaves on the basis of the function or the effect of the particles with the low specific Volume resistance in the development step (in which an electric field with a relatively high Strength is applied) as if it were a developer with a low volume resistivity while in the image transfer step (in which an elec-

Soldering field applied with a relatively low strength the developer behaves as if it were a developer with a high volume resistivity were. Consequently, despite the use of uncoated paper with a comparatively low specific Volume resistance can be obtained in both development and image transfer .

According to the invention an electrophotographic 25verfahren the type described above is further provided with which in particular a predetermined optimal ratio of particles having a high volume resistivity to particles having a low volume resistivity on the developing sleeve during the unloading ³⁰ winding and the image transfer steps can be obtained , with one or both of the particles being supplemented or refilled if necessary.

According to the invention, in a developing system in which the developer ^35, which remains on the photoconductor,

after an image transfer is recovered and reused, this is achieved by being in a developer container a developer is added and refilled that has the same mixing ratio of particles with a high specific Resistance and those that have a low specific resistance such as the mixing ratio of the developer, which has been transferred to a sheet of copy paper, while in a development system in which the developer, which remains on the photoconductor after development is removed without being recovered, this is achieved by replenishing and replenishing a developer that has the same mixing ratio of particles with a high volume resistivity and those with a low volume resistivity as the mixing ratio of that applied to the photoconductor Developer has

The invention is described below on the basis of preferred embodiments ungs forms explained in detail with reference to the accompanying drawings. Show it:

Fig. 1 shows the relationship between the change in volume resistivity of particles A with high

specific volume resistance and the change <;
a.s applied electric field the relationship between the change in volume resistivity of particles B with a low volume resistivity and the change in an applied electric field, as well as the relationship between the change in volume resistivity of a mixed developer, which according to the invention of particles A with a high specific volume resistance and particles B with a low specific volume

^ 5 resistance, and the change in one

applied electric field;

Fig. 2 shows the relationship between the change in volume resistivity of a mixture of Particles A with a high volume resistivity and particles B with a low one specific volume resistance and the proportion of particles A to the total amount of both particles A and B;

3 shows a schematic representation of the behavior of the particles with a high specific volume resistance and the particles having a low volume resistivity of a mixed one Developer during the development step;

4 shows a schematic representation of the deposition state of particles a with a high specific! Volume resistance and particles b ^{1 with low}

drigem specific. The volume resistance of a mixed developer on the surface of a photoconductor, the particle size of the particles b ^{1 being} larger than that of the particles a;

Fig. 5 after a development -a schematic representation-

l.

development of the deposition state of particles a with a high specific volume resistance and of particles b ¹ with a low specific volume

Volume resistance (as shown in FIG. 4 30

are) on a sheet of copy or transfer paper;

Fig. 6 is a schematic representation of the deposition status of particle a with a high specific

Volume resistance and of particle b with a 35

low volume resistivity of a mixed developer on the surface of a

Photoconductor, the particle size of the particles b being smaller than that of the particles a;

7 shows a schematic representation after a development the state of deposition of particles a with a high volume resistivity and of particles b with a low volume resistivity (as shown in FIG. 6 are) on a sheet of copy or transfer paper;

Fig. 8 shows the relationship between volume resistivity of two mixed developers each, each with two types of particles with different

have different resistivities and the applied electric field;

9 shows the relationship between the quantitative ratio of particles B to particles A on a photo

head and the quantitative ratio of particles B to particles A on a developing sleeve;

Fig. 10 is a schematic representation of the main parts of a Embodiment of an electrophotographic copier, that can be used according to the invention, and

Fig. 11 is a perspective view of a wiping member

of the electrophotograph 30 shown in FIG

see copier.

First, the principle of the invention will now be described. As stated above, in an electrophotographic Process in which a latent elektrosta-35

table image is generated on the surface of a photoconductor and the latent, electrostatic image by means of a

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A magnetic developer, which is magnetically attracted to a developing sleeve in the form of a magnetic brush, is developed by applying a comparatively high electric field, and in which the developed image from the surface of the photoconductor to a sheet of uncoated paper is applied when a comparatively low electric field is applied When a developer having a low volume resistivity is used, electric charges are induced on the surface layer of each developer particle due to the low resistivity of the IQ developer, and the developer particles are then applied to the latent electrostatic image in the developing step. In this way, a high development efficiency can then be obtained.

However, when the developed image from the surface of the photoconductor on a sheet of uncoated paper with a relatively low specific electrical continuity or volume resistance (for the sake of brevity, we will only speak of specific resistance in the following is) transferred, the electric charges of the developer particles easily flow through the paper, and consequently the image transfer efficiency is significantly lower and the quality of the developed image is significantly poorer.

In contrast, when a developer having a high specific resistance is used in the above-described Electrophotographic process is used, the image transfer efficiency due to the high specific Resistance can be increased. However, due to the high specific resistance, none can be sufficient for development electrostatic charges on the surface layer of the developer particles applied to the developing sleeve are induced, and consequently the development efficiency is considerably lower. The result is

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thus the overall picture quality is bad.

The above facts show that when developed in the above-described electrophotographic Method, a developer with a comparatively low, specific resistance can be used should, while he has a high specific Should have resistance. According to the invention, a magnetic toner having a specific resistance is provided.

i 3

see, which is not smaller than 10 JL cm. This magnetic one Toner with such a high specific resistance will be referred to as Particle A hereinafter. Furthermore is an electrostatic induction promoting agent having a resistivity not higher

jicm is. This agent having such a low resistivity will be referred to as particle B hereinafter .

These two kinds of particles A and B are mixed so that a developer having the above-described required properties is obtained, which in the developing step (in which an electric field of a comparatively high strength is applied) behaves as if it were a developer with a low resistivity, and which in the image transfer step (in which an electric field of a comparatively low strength is applied) behaves as if it were a developer with a high resistivity.
30th

The following describes examples of developers made from such particles A and B which can be used according to the invention are.

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example 1

Particle A:

70 parts by weight of Piccolastic D-125 (one of the Esso Chemical Co., Ltd. manufactured polystyrene) and 30 parts by weight of magnetite are mixed. The mixture is then worked through or kneaded, whereby heat is applied by means of heating rollers. When the mixture cools down, it turns to Powder ground, and the powder is sorted by size, so that particles A with a particle size of 50μΐη to 30μΐα, where the average particle size is 15μπι, and which has a specific resistance of 4x10 jvcm have to be received.

Particle B:

Magnetite Fe-O ₄ with a particle size of 1 μm to 10 μm with an average particle size of 5 μm was used as particle B. The specific resistance of the particles B

was 3x10 j "Lcm.

Developer No. 1-1

70 parts by weight of the particles A and 30 parts by weight of the particles B were mixed, thereby producing an according to the invention usable developer No. 1-1 was prepared. 25th

How the resistivities of Particles A and B and Developer No. 1-1 change when the strength of the applied electric field is changed, was investigated. The results are shown in FIG. How out 30th

As seen in Fig. 1, the specific resistance of the particles A was relatively high and changed little, even when the strength of the applied electric field has been changed as shown by curve A, during the specific resistance of the particles B is relatively low and decreased significantly as the strength of the applied electric field was increased, as shown by curve B

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is placed so that the particles B behaved as if they were essentially electrically conductive particles in a relatively high electric field range.

In contrast to the specific resistances of the two particles A and B, the specific resistance changed of the developer No. 1-1 from the particles A and B depending on on the strength of the applied electric field very strongly in a very wide range, as shown by the curve AB is shown. Especially when the strength of the The electric field applied to the developer was relatively small, so was the resistivity of the developer while when the strength of the applied electric field was large, the resistivity of the developer was high small.

Apparently, the developer No. 1-1 behaves in the developing section like a developer with a low specific resistance, if a comparatively high elec-

tric field is applied, while in the image transmission section, in which a relatively low electrical Field is applied, the developer behaves like a developer with a high specific resistance, so that consequently the requirements for the electrophotographic

see methods according to the invention are fully met. Of course the resistivity of a developer composed of particles A and B changes according to the ratio the amount of particles A to the amount of particles

In Fig. 2, the relationship between the change of the specific Resistances of the developer consisting of the particles A and B and the proportion of the particles A in presented to the developer when an electric field is applied ~ 3 4

that ranges from 5 χ 10 V / cm to 1x10 V / cm. Like on best seen from Fig. 2, when the ratio of the

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Particle A increases, the resistivity of the developer also increases.

Developer No. 1-2

90 parts by weight of the particles A and 10 parts by weight of the particles B are mixed, thereby producing an according to the invention Usable Developer No. 1-2 was created.

Developer No. 1-3

Magnetite with an average particle size of 10μίη was used as particle B. The specific resistance the particle B was 3 χ 10 Ω · cm. It became 70 parts by weight of the particles A and 30 parts by weight of the particles B are mixed, whereby a usable according to the invention Developer No. 1-3 was created.

Example 2

Particle A-2

As the particle A-2, the particle A used in the developer No. 1-2 was used.

Particle B-2

30 parts by weight of Piccolastic D-125 (one of the Esso Chemicals Co., Ltd. produced polystyrene), 60 parts by weight of Miagnetit and 10 parts by weight of carbon black. the Mixture was worked through and kneaded while applying heat by means of heating rollers. After the mixture has cooled down, the powder was ground, and the powder was classified according to size so that particles B-2 had a particle size from 5 to 20μπι with an average particle size

of 10μπι and with a specific resistance of 1x10 ./ern were received.

Developer No. 2-1

50 parts by weight of the particles A-2 and 50 parts by weight of the particles B-2 were mixed, whereby a according to the invention

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Finding Usable Developer No. 2-1 was created.

Developer No. 2-2

80 parts by weight of the particles A-2 and 20 parts by weight of the particles B-2 were mixed, thereby producing an according to the invention Applicable Developer No. 2-2 was created.

Example 3

Particle A-3

There were 34 parts by weight of a styrene-acrylate copolymer (manufactured by Sanyo Chemical Industries, Ltd.j, 65 parts by weight of magnetite and one part by weight of spirit Black SB (a dye manufactured by Orient Chemical Co., Ltd.) was mixed. The mix was worked through and kneaded while applying heat by means of heating rollers. After the mixture had cooled, the powder was ground and the powder was classified according to size so that particles A-3 with a particle size of 5 to 30μΐη with an average Particle size of 20μπ \ and with a specific

14th
see resistance of 3 χ 10, Λcm were obtained.

Particle B-3 ·.

As the particle B-3, the particles used in Example 2 became B-2 used.

Developer No. 3-1

90 parts by weight of the particles A-3 and 10 parts by weight of the particles B-3 were mixed, thereby producing an according to the invention usable developer No. 3-1 was created.

Developer No. 3-2

70 parts by weight of the particles A-3 and 30 parts by weight of the particles B-3 were mixed, thereby producing an according to the invention usable developer No. 3-2 was created.

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Example 4

Particle A-4

There were 50 parts by weight of a styrene-acrylate copolymer

^ (Manufactured by Sanyo Chemical Industries, Ltd is) and 50 parts by weight of magnetite mixed. The mixture was worked through and kneaded by heating rollers Heat was applied. After cooling the mixture - it was ground into powder, and the powder was sized

^ sorted so that particles A-4 with an average particle size of 15μ and a specific resistance of 1x10 JX cm were obtained.

Particle B-4

There were 30 parts by weight of a styrene-acrylate copolymer (manufactured by Sanyo Chemical Industries, Ltd.), 60 parts by weight of magnetite and 10 parts by weight of carbon black mixed. The mixture was worked through and kneaded, with heat being supplied via heating rollers. After cooling

With the mixture, it was ground to powder, and the powder was sorted by size so that the particles 3-4 with an average particle size of 5jim and with a resistivity of 1 χ 10 jft.cm were obtained.

Developer # 4

There became 90 parts by weight of the particles A-4 and 10 parts by weight of the particles B-4 were mixed, thereby providing a developer No. 4-1 usable in the present invention.

Example 5

Particle A-5

The mixture of the same ingredients as in Particles A-4 was worked through, using heating rollers 35

Heat was applied. After cooling the mixture was they ground them into powder, and the powder was sized

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sorted so that the particles A-5 with an average particle size of 12μΐη and a specific resistance of 1 χ 10 item were received.

Particle B-5
As the particle B-5, the particle B-4 was used.

Developer No. 5-1

96 parts by weight of Particles A-5 and 4 parts by weight of Particles B-5 were mixed, thereby producing an according to the invention usable developer No. 5-1 was created.

Developer No. 5-2

93 parts by weight of Particles A-5 and 7 parts by weight of Particles B-5 were mixed, thereby producing an according to the invention Usable Developer No. 5-2 was created.

The developers No. 1-1, 1-2,
1-3, 2-1, 2-2, 3-1, 3-2, 4, 5-1, and 5-2 all had those

same characteristics as shown in Fig. 1, and
are thus useful in the electrophotographic process of the present invention. The developers described
are given as examples only, and a variety of developers usable in accordance with the invention can be prepared.

The process for preparing and producing particles
with high resistivity (hereinafter referred to as the
Particles AA) and particles with low specific resistance, (hereinafter referred to as particles
BB) ₍ which can be used according to the invention will now be summarized according to the experiments carried out by the inventors.

The particles AA were made by kneading a mixture of about 70 to about 35 percent by weight of a resinous material,

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! for example from polystyrene or a styrene-acrylic resin, and about 30 to about 65 weight percent of a magnetic material such as magnetite (Fe_O.}, and if necessary of a dye with the application of heat, and the mixture was then powdered with a Particle size from 5μπι to 30μπι with an average Particle size in the range from 10μΐη to 20μΐη ground while the particle size BB simply by pulverizing a magnetic material, such as magnetite, to par-

lOtikel with a particle size of 1μπι to 10μΐη with a average particle size in the range from 5 μm to 6 μm or by kneading a mixture of about 30% by weight of a resin material such as a styrene-acrylic resin, 60 percent by weight of a magnetic material such as magnetite and about 10 percent by weight carbon black Applying heat and turning the mixture into powder with an average particle size in the range from 1/5 to 1/2 the average particle size of the particles AA and with a resistivity of no more than 10 micrometers, preferably less than 1 χ

10 λ cm was milled.

When only the magnetic material is used as the particles BB, 90 to 70% by weight of the particles become AA mixed with 10 to 30 percent by weight of the particles BB, while if a milled mixture of the resinous material, the magnetic material and carbon black is used, 80 to 50 weight percent of the particles AA with 20-50 weight percent the particles BB are mixed, whereby a according to

mixed developers usable in accordance with the invention can be provided.

Referring to Fig. 3, the development process of the electrophotographic process according to the invention and the reason described in detail, why the described, developer usable according to the invention works so well

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work. In Fig. 3, a fixed internal magnet 1 is in a Developing sleeve 2 is arranged, which is rotated around the fixed internal magnet 1 and is grounded. One photoconductive layer 3 is also grounded. Between the developing sleeve 2 and the photoconductive layer 3 is a development gap 4 is formed. In the invention is the development gap 4 is preferably smaller than 1 mm and is preferably in the range from 0.1 mm to 0.5 mm.

In the development step 4, the particles A are those with denoted by a reference character a, and the particles B, denoted by a reference character b, in the manner arranged so that the particles b cover the surface of each of the particles a. Furthermore, in this development section the development of latent, electrostatic images that appear on the surface of the photoconductive layer

3 are created, carried out by electrostatic induction when a relatively high electric field is applied, and the particles b then serve to promote such electrostatic induction for development and to support. For development by electrostatic induction, the has in the development gap

4 introduced developers have a low specific resistance, i.e. it is electrically conductive, as stated above.

After development, however, the electrical charges on the developer particles must then be maintained as high as possible until the developed images are transferred from the surface of the photoconductor to a sheet of copy paper. On the other hand, the specific resistance of the developer particles must be high enough to hold back the electrical charges. In particular, it must not be smaller than 10 x cm. In particular, when the specific resistance of the developer particles is less than 10 / tem-, electrical charges flow from the developer particles

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easily when the developed image is transferred from the surface of the photoconductor to the copy paper, and hence the degree of image transmission is then considerably lower.

^ When the potential of the first charges applied to the photoconductor is 1000V and the development gap
4 is 1mm, the electric field applied to the developer particles at the time of development is approximate

4th
10 V / cm. If a developer consisting only of particles A

■ ^^ is used under the electric field of 10 V / cm

14 r
its specific resistance is 10 item high, which is evident from the relationship between the specific resistance of the
Developer and the applied electric field can be seen, which is shown by a curve 5 in FIG. When the resistivity of the developer is 10 ^ 2cm high
is, an image development by an electrostatic
Induction cannot be performed at all. To get through
electrostatic induction to successfully perform image development under the above conditions

the specific resistance of the developer

4th
at an electric field of 10 V / cm no higher

than 10% cm.

The relationship between the resistivity of the

Developer No. 1-1 described above, which consists of 70 parts by weight of Particles A and 30 parts by weight of Particles B, and is the applied electric field
represented by a curve 6 in FIG. As can be seen from curve 6, the particles B serve to reduce the electrical

see induction in the developer to encourage, and the specific electrical resistance of the developer is less than 10-Äcm with an electrical field of 10 V / cm. Through this if an electrostatic induction is sufficient for image development at a specific electrical resistance

_{β /)}

stand created that is smaller than 10> lcm.

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The exact mechanism or sequence of how the particles A act as an electrostatic induction promoting agent, is not known. It is likely that the particles B work as electrodes. When the diameter each of the particles B 10 is μπι and if the potential of the electrical charges applied to the photoconductor 1000V, the electric field applied to each particle B is essentially 10V / cm, and hence it is assumed that the total resistivity of the developer is not higher than 10 J »icm.

In the invention, the ratio of the particle size of the particles A to the particle size of the particles B is an important one Factor. As stated above, the particle size is the Particle A larger than particle B “The reason for this will now be explained in detail.

If the particle size of the particles B is larger than that of the particles A, the particles A (indicated by a

20) and the particles B, / which are denoted by b 'in FIG. 4, are distributed on the surface of a photoconductive layer 3 as shown in FIG. When viewed under the microscope, the comparatively large particles b ^{1 are distributed} from place to place like rocks, between which particles a are arranged. When a developed image made of the particles a and b 'is transferred from the surface of the photoconductive layer 3 to a sheet of copying paper, not all of the particles b "having a relatively low resistivity are transferred from the surface of the photoconductive layer 3, but some of they remain on the photoconductive layer 3. As a result, this means that the image transferred onto the copy paper has visibly not transferred parts from place to place, which the

3 ^{correspond to 5} non-transferred particles b 'with a relatively large diameter, as shown in FIG. - 20 - ·

When the particle size of the particle B is smaller than that of the particles A / they become as shown in Fig. 6, distributed on the photoconductive layer 3, the particles A being denoted by a and the particles B being denoted by b. the smaller size of the particles b leads to no difference in the image transfer efficiency. However, if that developed Image transferred onto a sheet of copy paper are untransferred particles b as shown in FIG. 7 are, much less clearly visible on the copy sheet than in the case shown in FIG Comparison of the untransferred column L can be seen on the two sheets of copy paper. For a better one Image quality therefore the particles B must be smaller than the particles A.

In the electrophotographic process of the present invention the quantitative ratio of the particles A and the particles B in the developer is very important to the object of the invention to reach. However, as stated so far, due to the different resistivity between the particles A and B, the transfer rates of the two kinds of particles from the photoconductive layer not the same on sheets of copy paper, and consequently the mixture of

25 ratio between the particles A and B in the on the Developer sleeve applied gradually.

In particular in a copier system in which residual developer on the photoconductor is recovered and transferred to a

30 is returned to the developer tank, the percentage increases of particles B gradually increases, since less of them are transferred than of particles A. With this method it is, however, a requirement that must be met that the mixing ratio of particles A and B is essentially

³⁵ union is constant or within a predetermined reasonable range.

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In order to meet this requirement, a method is possible the amount of particles A and that of particles B to be replenished and replenished in the developer per unit of time are to be controlled separately by instantly determining the mixing ratio between the particles A and B applied to the developing sleeve. However is this procedure is not practical.

In practicing the invention, the following two developer replenishment methods have been found to be effective proven. The first method is applicable in a development system in which the developer based on the Photoconductor left after an image transfer is recovered and is used again. This method uses a developer that has the same mixing ratio of the particles A and B as the mixing ratio of the particles A and B in the one on a sheet of copy paper Has transferred developer, refilled in a developer container, whereby the originally predetermined Mixing ratio of the particles A and B can be maintained on the developing sleeve.

The second method is created for a development system in which the developer remaining on the photoconductor after the image transfer is removed, but for reuse is not recovered. This method uses a developer that has the same mixing ratio from the particles A and B as the mixing ratio of the particles A and B in the form on the photoconductor of a toner image applied developer, refilled in a developer container, whereby the originally specified mixing ratio of the particles A and B can be maintained on the developing sleeve

can.
35

With reference to FIG. 10, one can be used according to the invention Development facility explained. In Fig. 10 are around one

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Photoconductor drum 30, in the direction of rotation thereof, a loader 5 for the first loading of the photoconductor drum 30, an exposure station 6, a development station 7, a charger 8 for image transmission, a charger 9 for erasing electrical Charge on the photoconductor drum 30 and a cleaning device 10 arranged.

At a position of a developing sleeve 2 which is opposite to the developing section 7 with respect to the developing sleeve 2, a developer replenishing container 11 is arranged. There is also a scraper 12 and a doctor blade 13 arranged around the developing sleeve 2 in the direction of rotation thereof. The scraper 12 is arranged so that his front cutting part resiliently sprung / on the circumferential surface the developing sleeve 2 and has a number of narrow windows 14. The doctor blade 13 is arranged so that its front cutting part has a small distance from the peripheral surface of the developing sleeve 2.

The developer from the particles · * A and B is made by the magnetic Attraction of fixed magnets 1 arranged inside the developing sleeve 2 to the peripheral surface the sleeve 2 is tightened and becomes the stripper 12 conveyed when the sleeve 2 is rotated. The developer attracted to the sleeve 2 is removed by the wiper 12 scraped off the surface of the sleeve 2 and at the same time mixed well. The well-mixed developer goes through the narrow window 14 and is then conveyed to the doctor blade 13, where the developer, which in Form of a brush has been attracted to the sleeve 2, is brought to a predetermined thickness and then accordingly the rotation of the sleeve 2 of the developing station 7 is fed. That way, the developer gets away from the Developing sleeve 2 is transferred to the surface of the photoconductor drum 30 so that a latent electrostatic image is developed on the surface. The developed image

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is then from the surface of the photoconductor drum 30 in the image transfer section using the for image transfer provided loader 8 onto a sheet of copy paper S -

In a development system in which the developer left on the photoconductor after image transfer is removed without being recovered, the residual developer on the photoconductor drum 30 is through the Cleaning device 10 removed. In contrast to this, in the development system in which the after a Image transfer remaining developer on the photoconductor is recovered and reused Cleaning device 10 is not provided. Rather, the residual developer on the photoconductor drum 10 is attached to the peripheral surface the sleeve 2 tightened, so that thereby the photoconductor drum 30 is cleaned. As a result, in the last-described development system, image development becomes and transmission during the first revolution of the

on ■

* ^w photoconductor drum 30 and cleaning of drum 30 performed during its second revolution. In other words, this is a system in which a copy is made at two revolutions.

In Fig. 9, the relationship between (1) is the change in the ratio of the particles B in the developer which is made up of the particles A deposited on the developing sleeve 2 and B, and (2) the change in the ratio of particles B in the amount on the surface of the photoconductor

drum 30 assigned developer shown “This relationship is represented by a curve 15.

Further, in Fig. 9, the relationship between (1) is the change the ratio of particles B in the developer, 35

which consists of the particles A and B applied to the sleeve 2, and (2) the change in the ratio of the particles

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Article B shown in the developer, which is over the photoconductor drum has been transferred to a sheet of copy paper. This relationship is shown by a curve 16. As can be seen from curves 15 and 16, in the image developing step, a developer having a mixing ratio is used from the particles A and B, which is different from the original mixing ratio of the applied to the sleeve 2 Developer differs, transferred to the surface of the photoconductor drum 30. Similarly, will in the image transferring step, a developer having a mixing ratio of the particles A and B that is differs from the mixing ratio of the developer applied to the surface of the photoconductor drum 30, is transferred onto a sheet of copying paper, and hence this mixture ratio is different from the mixture ratio of the developer applied to the surface of the developing sleeve 2. As stated earlier and as can also be seen from Fig. 9, the particles B are consumed less than the particles A. Consequently become in the course of numerous copying processes the Particle B in the developer applied to the sleeve 2 more. In other words, the ratio · of the particles B in the developer applied to the sleeve 2 becomes larger in the course of numerous copying operations, whereby the the resistivity of the developer decreases with time, and consequently the copy quality deteriorates.

Attempt 1

Developer No. 1-2 (see Example 1) composed of 90 parts by weight of Particles A having an average particle size of 15μΐη and 10 parts by weight of the particles B with an average particle size of 5μπι consists, was in the developer replenishing container 11 in an amount housed, with which at least the circumferential surface of the Development sleeve 2 be covered v / who can. Before this Attempt the developer was introduced into the container 11,

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was neither on the sleeve 2 nor in the container 11 developer available.

When starting the copying process, the peripheral area of the The developer sleeve 2 is uniformly covered with developer. The amount of developer with which the peripheral surface of the sleeve 2 can be covered was constant. The developer applied to the sleeve 2 consisted of 90 parts by weight of the particles A and from 10 parts by weight of the particles B, their Mixing ratio was exactly the same as that of the developer initially put in the container 11 is.

After image development, the mixing ratio of the particles A and B became the developer on the surface of the photoconductor 30 measured. As a result, it was found that the developer was composed of 93 parts by weight of Particles A and 7 Parts by weight of the particles B, as shown in FIG. In the image transfer step, the design was

The winder on the photoconductor 30 was then transferred to a sheet of copy paper, and the mixing ratio became again of the particles A and B of the developer were measured on the copy paper. As a result, it was found that the developer from 96 parts by weight of the particles Ä and four parts by weight the particle B existed as shown in FIG.

When the developer that remains on the photoconductor drum 30, was recovered and reused, a developer composed of 96 parts by weight of Particles A and

four parts by weight of the particles B existed, their mixing ratio was exactly the same as that of the developer transferred to the copy paper, the developer refill container 11, whereby the original mixing ratio of particles A and B (i.e. 90:10) of the

Winder was retained on the tube 2 and one

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High quality copy has been obtained. It must be pointed out again that the amount of developer with which the peripheral surface of the sleeve 2 can be covered to substantial was constant.

When the developer that remains on the photoconductor drum 30 after after image transfer was removed without being recovered, a developer composed of 9 3 parts by weight of the particles A and 7 parts by weight of the particles B, the mixing ratio of which was exactly the same as the mixing ratio of the developer to be added to the Surface of the photoconductor drum 30 had been transferred to a developer replenisher 11, whereby the original mixing ratio of particles A and B (i.e. 90:10) of the developer on the sleeve 2 is maintained remained, and thus also: another copy of high quality

'was received.

Attempt 2

² ^ Experiment 1 was repeated, replacing developer no.1-2 with developer no.1-3, which consists of 70 parts by weight of particles A and 30 parts by weight of particles B. The developer applied to the sleeve 2 consisted of 70 parts by weight of the particles A and 30 parts by weight of the particles B, the mixing ratio of which was exactly the same as that of the developer j initially placed in the container 11.

After image development, the mixing ratio became

the particles A and B in the developer on the surface the photoconductor drum 30 is measured. As a result, it was found that the developer was composed of 80 parts by weight of Particles A and 20 Parts by weight of the particles B existed (see Figure 9). at

the image transfer step became that on the photoconductor 35

30 applied developer then to a sheet of copy paper and the mixing ratio of the particles A and B in the developer on the copy paper was measured.

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³⁴ 3H0639

-Vf-

As a result, it was found that the developer was composed of 90 parts by weight of Particles A and 10 parts by weight of Particles B. (see Fig. 9).

When the developer remaining on the photoconductor wire 30 was recovered and reused a developer consisting of 80 parts by weight of the particles A and 20 parts by weight of the particles B, their mixing ratio is exactly the same as the mixing ratio of the developer transferred to the sheet of copy paper, supplied to the developer replenishing container 11, whereby the original mixing ratio of the particles A and B (i.e. 70:30) of the developer applied to the sleeve 2 was obtained and another high quality copy was obtained became.

When the developer that remains on the photoconductor drum 30, was removed after an image transfer without being recovered, a developer composed of 90 Parts by weight of the particles A and 10 parts by weight of the particles B, the mixing ratio of which is exactly the same is like the mixing ratio of the developer transferred to the surface of the photoconductor drum 30 to the developer replenisher 11, with the original mixing ratio of particles A and B (i.e. 70:30) of the developer was retained on the sleeve 2 and another high quality copy was also obtained.

Attempt 3

^ow Experiment 1 was repeated, with developer no.1-2 being replaced by developer no.4, which consists of 90 parts of particles A-4 and 10 parts of particles B-4. The developer applied to the sleeve 2 consisted of 90 parts by weight of the particles A-4 and 10 parts by weight of the particles B-4, the mixing ratio of which was exactly the same as that of the developer initially placed in the container 11.

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3U0639

After an image development, the mixing ratio became of the particles A and B in the developer on the surface of the photoconductor 30 are measured. It turned out that the The developer consisted of 93 parts by weight of Particles A-4 and seven parts by weight of Particles B-4. At the image transfer step the developer on the photoconductor drum 30 was transferred to a sheet of copy paper, and it the mixing ratio of the particles A-4 and B-4 in the developer on the copy paper was measured. Here The developer was found to be composed of 96 parts by weight of Particles A-4 and four parts by weight of Particles B-4 duration.

When the developer that remains on the photoconductor drum 30, was recovered and reused, became a developer composed of 96 parts by weight of Particles A-4 There are four parts by weight of the particles B-4 in their mixing ratio is exactly the same as that of the developer transferred to the sheet of copy paper, the container supplied, the original mixing ratio of the .Particles A-4 and B-4 (i.e. 90:10) of the developer on the Sleeve 2 was obtained and thus another high quality copy was obtained.

When the developer that remains on the photoconductor drum 30, after image transfer was removed without being recovered, a developer composed of 93 Parts by weight of particles A-4 and seven parts by weight of particles B-4, the mixing ratio of which is accurate

was the same as that of the developer transferred to the surface of the photoconductor drum 30, the developer replenisher 11 supplied, the original mixing ratio of particles A-4 and B-4 (i.e. 90:10) des

Developer was retained on sleeve 2, and 35

another high-quality copy has also been preserved.

Multiple copies were then made using the process

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of experiment 3 was repeated, and it was found that that the particle size of the particles A-4 gradually increases in the course of the repeated copying process and the particles A-4 with the larger particle size in the developer gradually increased. Consequently, the The sharpness of the image obtained on the copy is somewhat worse in the course of the repeated copying processes,

an increase in the particle size of the particles A-4 in the course To prevent duplicate copying operations, the following experiment was carried out in which the particles A-4 were replaced by particles A-5, the average particle size of which was smaller than that of the Particle A-4.

Attempt 4

A copy was made under the same conditions as in Experiment 3. When the developer that is on the photoconductor drum 30 was left behind, recovered and reused, became developer # 5-1, which was made from 96 Parts by weight of the particles A-5 with an average particle size of 12μπι and from four parts by weight of the particles B-5 with an average particle size of 5μΐη, the mixing ratio of which was exactly the same like that of the developer transferred to the sheet of copy paper, supplied to the developer replenisher 11, wherein the original mixing ratio of the particles Ά-4 and B-4 (i.e. 90:10) of the developer was retained on the sleeve 2, and also over the course of several times

³ ^ brought copying continuously high quality copies were obtained.

When the developer that remains on the photoconductor drum 30, after an image transfer was removed without being recovered, Developer No. 5-2 became the from 93 parts by weight of the particles A-4 with an average Particle size of 12μπι and from seven genes

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parts of the particles B-4, their mixing ratio was exactly the same as that of the developer transferred to the surface of the photoconductor drum 30, the container

11 supplied, the original mixing ratio 5

of particles A-4 and B-4 (i.e. 90:10) of the developer was retained on the sleeve 2, and also over the course of several times copies of high quality can be obtained from repeated copying operations became.

In Experiment 4 there was an increase in the mean Particle size of particles A-4 and particles B-4 not and hence the sharpness of the copy image was maintained. In addition, 4 particles B-5 were used in the experiment, whose average particle size was the same 15

like that of particle B-4. However, particles can also be included a particle size smaller than that of the particles B-5 can be used.

According to the invention, as a particle with a high specific Resistance magnetic toner used. However, non-magnetic toner can also be used, its specific electrical resistance not higher than .10 μl is. For example, non-magnetic toner can also be used be det, which has 95 to 85 parts by weight of a styrene-acrylate copolymer and 5 to 15 parts by weight of carbon black, wherein the particle size is in the range from 10μΐη to 30μπι, and less than 5 parts by weight of a dye may be added if necessary.

End of description

Claims (1)

Claims 1 “An electrophotographic process in which a developer in the form of a brush is attracted to the peripheral surface of a developing sleeve having magnets inside, to which developer attracted to the developing sleeve is supplied with an electrostatic latent image formed on an electrostatic latent image bearing member to develop the electrostatic latent image and in which the developed image is transferred to a sheet of copying material, characterized in that the developer is a mixture of particles having a high volume resistivity not less than 10 JX cm and particles with a low volume resistivity not higher than 10 -h_ cm, and that the speci-VII / XX / Ktz - 2 - Έ (089) 988272 telegrams: bank accounts Hypo-Bank Munich 4410122850 Fish electrical resistance of the developer as a function the strength of an applied electric field in a range of low specific resistance, which enables the electrostatic latent image to be developed on the image-bearing part to a high degree Resistivity is changeable, which is an image transfer of the developed image from that of the latent image allows the load-bearing part to be attached to the sheet of copy paper. jQ 2. Electrophotographic process according to claim 1, characterized marked that the particle size of the particles with a high resistivity in the area from 5μΐη to 30μΐη, and that their average Particle size ranging from 1/5 to 1/2 the average particle size of the particles with a low specific resistance lies. 3. Electrophotographic process according to claim 1, characterized characterized in that the particles with a high resistivity are magnetic toners, and that the particles having a low resistivity are an electrostatic induction promoting agent are, which serves to make the developer electrically conductive at the time of development, the specific Resistance of the developer in the event of an electrical 4 tric field of not less than 10 V / cm not higher than 10 _o_ cm and not at the time of an image transfer 13th
less than 10, 0. cm is. 4. Electrophotographic method according to claim 2, characterized in that - that the particles with a high resistivity about 70 to about 35 Ge weight percent of a resinous material and about 30 to 65 percent by weight of a magnetic material. 35 5. Electrophotographic method according to claim 1, characterized in that the developer, the remains on the electrostatic latent image bearing member after image transfer, recovered and reused is, and that a developer that has the same mixing ratio of particles with a high and a has a low specific resistance as the mixing ratio of the two types of particles in the developer, transferred to the sheet of copying material in the course of repetitive copying on the developing sleeve is refilled, the original mixing ratio of the particles with a high and a low resistivity in the developer can be maintained. 6. Electrophotographic process according to claim 1, characterized characterized in that the developer applied to the electrostatic latent image bearing member remains after image transfer is removed without being recovered, and that a developer that the same Mixing ratio of the particles with a high and low resistance value as the mixing ratio of the two kinds of particles in the developer applied to the latent image bearing member, in the course of is supplemented by repeated copying operations on the developing sleeve, with the original mixing ratio the particles with a high and a low resistance value are retained in the developer can. 7ο electrophotographic method according to one of claims 5 or 6, characterized in that the average particle size of the particles with a high specific resistance in the developer ^ which has been used for the second time for a refill is smaller than the average particle size of the particles with ³ ^ a high resistivity in the developer used for the first time. 3140539 1 8. Electrophotographic method according to one of the claims 5 or 6, characterized in that the average particle size of the particles with a low specific resistance in the developer 5 second time used for a refill is smaller than the average particle size of the particles with a high resistivity in the developer used for the first time.