AU479217B2 - Developing device inan electrophotographic copying apparatus - Google Patents

Description

e 479.217

PATENT SPECIFICATION (21) 50, 47 1/72 -3 AUS TRALIA~f-

Class (52) 51.11 COp, 155ED Int. Cl. (51) G03G 15/10 t T sS

Application Number (21) 50471/72 Lodged (22) 22nd December, 1972.

Complete Specification entitled (54) DEVELOPING DEVICE IN AN ELECTROPHOTOGRAPHIC COPYING AFPARATUS

Lodged 22nd December, 1972. Accepted 8th December, 1976. Published 27th June, 1974.

Convention Priority (30) Japan 25th December, 1971. 880/72 29th December, 1971. 1236/72

Applicant (71) CANON KABUSHIKI KAISHA

Actual Inventor (72) SHIGEHIRO KOMORI, HIROSHI NITANDA and TOSHIHIDE HDA

Related Art (56) 425497 (17418/70) 51.1-1 416950 (22437/67) 51.1-1, 56.5 416279 (1484/66) 51.1-1, 52.5

it known The following statement is a full description of this invention,-including the best method of performing to us F. D. Atkinson. G:vernment Printer Cnberra 11746/75-L

X858-65-3D-13 P. C.

47 I:

This invention relates to a developing device in an

electrophotographic copying apparatus of the liquid developing

type, and more particularly to a developing device in which masses of toner present in developing liquid composed of

carrier liquid and toner are dispersed to thereby maintain

the toner density constant.

In electrophotographic copying machines, the liquid development has been superior to the dry type development in

that the former is more efficient and can produce better

copies than the latter. The developing liquid used therefor is composed of carrier liquid and toner, and the toner must be maintained uniformly dispersed to provide good image reproduction. Further, in view of the gradual toner con- sumption caused by the developing process, it is also necessary during a long-time use to detect the toner density

at all times to maintain the developing liquid at a density

adapted for the image to be copied. 479. 217

47 1n2 For these purposes, it has heretofore been the practice to measure the density of the developing liquid by using photoelectric detector means comprising a lamp and a light receiving element. However, the photoelectric: detector means simply immersed in the liquid within a developer con- tainer as was done in the prior art would readily permit deposition of toner which in turn would cause density differences partly in the liquid. In addition, the toner which is ready to deposit would often adhere to a transparent member interposed between the lamp and the light receiving element, thereby reducing the detecting function of the detector means. Also, in another conventional arrangement wherein the photoelectric detector means is disposed outwardly of the developer container and the developing liquid is supplied by a pump, the developing liquid rarely stays in the detector means during inoperative condition of the apparatus so that the surface of the transparent member tends to dry up and permits residual toner to adhere thereto. For these and

other reasons, it has been difficult with such arrangement to ensure accurate density detection and to provide image re- production of constant and excellent quality by simply detecting the density and supplying a predetermined amount of toner. Furthermore, the developing liquid tends to evaporate during the inoperative condition of the apparatus to readily cause the toner in the carrier liquid to adhere and solidify. When the apparatus is restarted, such solidified toner may be admixed with a circulating flow of developing liquid which is supplied to developing electrode means, thus causing irregular image reproduction to take 47 9.217

50 .47 1" place or injuries to be'impar ed to the photosensitive medium. It is an object of the present invention to provide a developing device which ameliorates the above-noted dis- advantages and in the preferred form ensures image reproduc- tion of excellent quality. In general form the present invention is a developing device using developing liquid to develop an electrostatic latent image formed on the surface of an electrostatic image bearing member, said device comprising: a developing liquid

storage tank; a developing portion for contacting said electrostatic image bearing member with developing liquid; pumping means for supplying developing liquid from said storage tank to said developing portion; and means for con- trolling the density of the developing liquid, and having detecting means for detecting the density of the developing liquid, said detecting means including a detecting chamber immersed within the developing liquid within said storage tank, a developing liquid passage formed across said chamber and arranged to pass therethrough part of the flow of develop- ing liquid supplied by said pumping means.

4'19,2

47 1/712

The invention will become fully apparent from the following detailed description of a preferred form thereof

described in conjunction with the accompanying drawings, in which;

Figure 1 is a vertical cross-section through a portion of a basic form of the developing device according to the present

invention; Figure 2 is a plan view taken along line A-A in.Figure 1;

Figure 3 is a plane view taken along line B-B in Figure 1;

Figure 4 is a vertical section of an embodiment of

the density detector chamber;

Figure 5 is a transverse section taken along line C-C

in Figure 4; Figure 6 is a diagram of the electric circuit used in the device of the present invention;

Figure 7 shows, in vertical section, another embodiment of

the density detector chamber; Figure 8 is a transverse section taken along line

D-D in Figure 7; and Figure 9 shows a transparent member in the density

detector chamber provided with means for applying an electric

field.

479.217

471 /72 Referring to Figure 1, there is shown an embodiment

of the device according to the present invention, which

includes a developer container 1 for storing developing liquid

2 therein, a stirring impeller 3 located within the developing

liquid, a pump 4 located just below the stirring impeller 3,

and a motor 6 mounted on the lid 5 of the container 1 by means

of a strut 7. In the illustrated example, the stirring

impeller 3 and the pump 4 are mounted on a common motor shaft

8. A frame 9 supports the stirring impeller 3 and pump 4 and

is fixedly secured to the lid 5. An intake port 10 for the

pump 4 is formed in the frame 9, and a filter 11 is provided

across the entrance of the intake port 10 and faces the

stirring impeller 3. When rotated, the motor 6 drives the stirring

impeller 3 and pump 4 so that the stirring blades 31 produce

a stirred flow therearound which circulates through the

developer container 1 to agitate the toner deposited in the

container while part of the said flow is sucked into the

pump 4 through the filter 11 and intake port 10 and supplied via a pipe 12 to a developing portion. Referring to Figure 2, which is a plan view taken along line A-A of Figure 1, it is seen that rotation of the

stirring impeller 3 causes a flow of liquid oriented

laterally to the shaft 8 as indicated by arrows, and as

required, the flow may be directed so as to dually cross the path of the stirring blades 31. Reference is now had to Figure 3, which is a plan

view taken along line B-B of Figure 1. The stirring impeller 3 stirs the toner deposited in the container as described 479, 217

50 47 n2 previously, the toner being in the form of masses produced in the developing liquid in the described manner. These masses

of toner are made to move as a stirred flow around the impeller 3 and impinge on the filter 11 for re-dispersion or impinge on any masses of toner which might have already adhered to the filter, thus dispersing or displacing such older toner masses to thereby prevent them from adhering to the filter. The developing liquid is sucked into the pump 4 at a small rate while being filtrated through the filter 11 at the entrance of the intake port 10, so that only the toner free of masses is delivered to the developing part. The residual liquid once used for development or the liquid used to clean the surface of the photosensitive drum 14 may be collected in the container 1 for reuse. Any dust or other foreign material which may be present in such liquid is filtered to protect the photosensitive medium against damages. Since the pump 4 utilizes as its drive source a common motor with the stirring impeller, the former is desirably disposed just below the latter. The rapid rotation to of the stirring impeller 3 which is in the range of 2,000 liquid, 3,000 r.p.m. may cause air to be introduced into the thereby producing bubbles therein. If liquid with such

bubbles is supplied, it would reduce the pumping efficiency For and accordingly result in an uneven developing effect. be provided this reason, a partition plate 13 may preferably the liquid just above the stirring impeller 3 to isolate liquid from the air on the surface of the developing (see Figure 1). Figure 4 shows, in vertical section, a specific -7- 479,217

50 47 1/72 construction of the density detector portion forming part of

the density control means in the developing device of the

present invention. Figure 5 is a transverse section taken

along line C-C of Figure 4. A small compartment 26 for

detecting the density is defined in the developing liquid 2

contained in the developer container 1, and a passage 27

formed by a transparent material such as glass or the like

extends vertically across the compartment 26 so that part of

the fluid developing liquid supplied to the developing portion

from the pump 4 may be forced into the passage 27 via a

conduit 12i, as required.

Photoelectric means 28, 29 are disposed on the

opposite sides of the passage 27. Even during the inoperative

condition of the apparatus, the developing liquid remains in

the passage 27 to thereby reduce the possibility of toner

adhering to and contaminating the transparent passage wall

portion between the lamp 28 and the light receiving element

29. Also, the developing liquid passing through the

transparent passage 27 is a sufficiently stirred mixture of

carrier liquid and toner delivered to the developing portion, as described previously, and this ensures proper detection of

the liquid density. Figure 6 shows the electric circuit of the density

control means used with the present invention. First, for

a body of developing liquid preset to a predetermined density,

a variable resistor VR is adjusted with respect to the lamp

28 so that the potential set by fixed resistors R2, R3 and

variable resistor VR and the potential set by fixed resistor

Rl and light receiving element such as CdS cell 29 are

completely equal to each other. By so setting, the input

479.217 terinals terminals and 47 !n of an operational amplifier (hereinafter referred to as OPA) 30 are at the same potential, so that the output is at zero (low) level to render a transistor Trl non- conductive. In this position, an electromagnetic solenoid L is inoperative and the valve of the toner supply container remains closed. If the density of the developing liquid 2 becomes lower, the quantity of light received by the light receiving element 29 will be increased and the resistance value of this element will be decreased. This will destroy the balance of the bridge to thereby cause the OPA 30 to produce its output which will render the transistor Trl con- ductive. As a result, the electromagnetic solenoid L will be energized to open the valve of the toner supply container to allow toner to be mixed with the developing liquid so as to restore the predetermined density. When the predetermined density is reached, the bridge including the light receiving element 29 will be balanced to bring about zero output of the OPA 30 again, thus deenergizing the electromagnetic solenoid L to close the valve of the toner supply container. Figure 7 shows another form of the density detector portion in vertical section, and Figure 8 is a transverse section taken along line D-D of Figure 7. The flow of developing liquid may sometimes carry bubbles therein which would cause an error in the density detection. In the embodiments shown in Figure 4 or 7, the passage 27 is located far below the liquid level as shown in Figure 7 or located a little below the liquid level as shown in Figure 4, so as to permit the bubbles to escape upwardly and thereby prevent any error from occurring in the 47 9, 217 density detection. 5 O, 1/72 7 0, 471 In spite of such designs, contamination by adhering toner would be unavoidable during a long-time use, and especially the density detector portion would suffer from a detection error which leads to a serious inconvenience.

The contamination imparted by toner is primarily

attributable to the adhering action of the toner to the

transparent member forming the passage. If the immersion of

the transparent member in the developing liquid continues for

long hours, the adhering action would increase the amount of

toner adhering and relatively reduce the transmittivity of

the transparent member. Secondly, if the wet transparent

member contacts air, toner adhering thereto would be dried up

to form layers such as irregular black lateral stripes where

the toner is black in appearance. Such black layers would not

be soluble even if they were re-immersed in the developing

liquid, and repetition of such condition would gradually

increase the thicknesses of the black layers to hamper the

transmission of light through the transparent member.

According tokthe present invention, the contamination

resulting from the above-described causes may be prevented by

using such means as will be described hereunder. A coating

of low surface tension material is applied to that side of

the liquid density detector portion which is exposed to the

developing liquid. When such coating of low surface tension

material is contacted by the developing liquid which has a

higher surface tension than the coating, there will occur a

phenomenon that the mutual wetting between the former

material of low surface tension and the latter material of

higher surface tension is very much aggravated. By utilizing 479. 2 1 7 such phenomenon, it 50 47 1/72 is possible to prevent the toner in the developing liquid from adhering to the transparent member.

Various types of carrier are available for use in

the wet development, and most of them have a paraffin mole- cular structure and generally presents a surface tension in

the range of about 25 to about 35 dyn/cm. In contrast, materials sufficiently usable to reduce the surface tension

of the transparent member below the foregoing range will be

enumerated below.

A first material is silicone oil which is a mixture of methyl hydrogen polysiloxane shown by formula below (produced and sold under the trade name of POLON MR by

Shinetsu Kagaku Co., Ltd. of Japan) and dimethyl polysiloxane shown by formula below (available from the same man- ufacturer under the trade name of POLON MG or POLON MN).

H

(CH 3 3 Si 0 [Si 0 Si(CH3 3 (1)

H

(CH3 3 Si 0 [Si ]n si(CH3 3 (2)

CH 3

Florine materials of low surface tension include:

per-fluorocarboxylic acid chrome complex salt [Rf.COOCr 2 OH]4+

(Rf=CF3 C4 F 9 (eg. trade name of FC804, produced by Minnesota Mining and Manufacturing acrylic acid fluoro- alkyester polymer [-CH2 CH(C00 CH 2 R'f n (R'f=CF3

C4 F 9 (eg. trade name of SCOTCH GARD, produced by Minnesota

Mining and Manufacturing poly-IB.IH pentadecafluoro-

479, 2 1 7

1/72 50 47 name produced by the octyl methacrylate (eg. trade FC706,

same company); and per-fluoroalkyester polymer IRf.CH2 CHCH 2 OH

OOCCR'=CH 2 (Rf=C 3F7 C1 0 F 2 1 (eg. trade name FP-81,

produced by Sumitomo Kagaku Co., Ltd.). All these materials

are sold in liquidous form. In the embodiment of the present

invention, acrylic acid fluoroalkyester polymer has been

found more effective than silicone oil materials probably

because it has a surface tension of 11 to 15 dyne/cm. These materials actually present little or no

appreciable difference in the physical strength of the formed

coating as long as the surface of glass or plastic material

forming the transparent member is sufficiently cleaned.

Exceptionally, however, some partial wear has been found when the developing liquid has flowed through the transparent

member at a very high speed. In practice, such high speed of

flow is hardly possible, but a fluorine coating material surface provided with a reactivity with respect to the glass (eg. trade name L-1653 or L-1668 commercially available from

Minnesota Mining and Manufacturing Co.) is highly effective

against the wear, although this material has a surface

tension somewhat higher than the aforesaid fluoroalkyester

polymer. It should be noted that a mixture of the above-

enumerated various low surface tension materials is also

highly effective. In order that the characteristic of the detector

portion using the foregoing materials may be better understood,

some examples of our experiments will be shown below.

Experiment 1: The transparent member was formed of glass or acryl

-12- 479.2 17

50 471/n2 plate, with the detector'portion clearance set to 1mm, and

the density of the developing liquid was adjusted so that it

might transmit 50% of light. Each of the foregoing materials was applied to the surface of the transparent member to form

a coating having a thickness of 1 to 6 microns. A different transparent member, formed of the same material but subjected

to no such treatment, was continuously immersed in the

developing liquid, and the total transmittivity of this

member in the developing liquid was measured at each lapse

of 1,000 hours, 2,000 hours and 4,000 hours. The results are shown in Table 1 below. The extent of contamination A T imparted to the transparent member by the developing

liquid is expressed: A T=TO T where T is the trans- mittivity at the beginning of the measurement and T is that after the lapse of a predetermined time.

-13- 479,217

47 172 Table 1: TransmittivitY Change

TransmittivitY change with time(%)

Base Coating Manu- -S) 0 1000 2000 3000 member materialI facturer

non-

treated

Polon Shinetsu

MR Kagaku 50 49 47 44

50 50 49 48 Glass FC-804 3M (Blue FC-706 Plate Fp-81 Daikin Glass) 50 50 50 49 Kogyo

50 49 49 48 L-1653 3M

non- treated 50 I 42! 361 19 Polon Shinetsu

47 43 MR Kagaku 50 49 47 lAcryl FC-804 3M 50 50 49

plate IFC-706 3M 50 50 50

(trade- Daikin

name Kogyo 50 50 3M 50 49 48 !L-1653

Co. Note: 3M=Minnesota Mining and Manufacturing

-14- 479.,217

Experiment 2: 50. 4 7 102 The same device as that used in Experiment 1

was used and immersed in the similarly conditioned

developing liquid for 8 hours, whereafter it was removed

from the liquid and dried for 30 minutes by a drier at 60 C,

and then the transmittivity thereof was measured by the

use of a spectral photometer. Table 2 below shows the

results of the measurements effected at every five, ten,

fifteen and twenty cycles, it being understood that the

above-described test process is one cycle.

479.217

Table 2: Transmittivity Change

Transitti rity change with cycle

Base Coating 0 material Mnu- 15 member fact urer 0 5 10

non- 94 75 54 31 19 treated

Polo Shinetsu 83 83 MR K Kagalu 89 86 Glass FC-804 31M 92 91 j89

(Blue FC-706 3H 92 191 191 191' 190 plate Fp-81 Daikin glass) Kogyo 92 91 go I9 8

L-653 3H 93I187 187 187 187 non-

treated 96 173 15 132 114 IPo ion Shinetsu 91 86 182 82 82 KR Kagaku

34 92 91 89 89 89 kcryl FC-804

plate 3H 92 91 90 90 FC-706 (q'rade- Fp-6l Daikin name j Koyo 92 90 90 90 88 "Sumipex" 93 88 86 86 86 L-1653 3H

47 ,217

50 47 1 n It can be seen'from Experiments 1 and 2 that a

great difference in transmittivity is provided between the

transparent member having the surface thereof coated with a

low surface tension material and the transparent member

having no such coating. However, since toner particles are stirred together

with the oil of high insulation resistance to develop the

electrostatic latent image on the photosensitive medium,

they are provided with electrostatic charges of the opposite

polarity to the charges of the electrostatic latent image, due to the friction occurring between the toner particles

and the oil. Because of the electrostatic power thus

imparted to the toner particles and the adhesive property

inherent to the toner particles, some toner particles may

also be found to adhere to the surface of the transparent

glass or plastic material forming the passage 27 for

detecting the density of the developing liquid. 1 lfu W44 i According t 6the present invention, to prevent these the contamination of the transparent member arising from

reasons, either a potential opposite in polarity to the

electrostatic latent image to be developed but identical an AC with the toner particles in the developing liquid or desired. voltage may be applied to the transparent member, as away The applied voltage acts to repulse toner particles which from the passage portion of the transparent member particles provides a light path, thus preventing the toner

from adhering to such portion. Figure 9 shows a specific embodiment of the realizing detector portion which is provided with the means

the above-described prevention of the toner contamination.

-17- 479, 2 17

47 1/72 In this embodiment, both the lamp 28 and the light receiving

element 29 are arranged at one side of the passage 27 of

the transparent member. That side of the passage 27 which

is adjacent to the photoelectric means 28, 29 is provided

by a plate of Nesa glass 31 coated with a transparent

conductive material such as tin oxide or the like. The other

side is provided by a reflector plate 32 having a mirror

surface formed of evaporated metal or the like. The

developing liquid 2 delivered from the supply means such as

pump 4 (Figure 1) may further be directed into the passage

27 via conduit 121, as desired.

On the other hand, an AC field or a field of the

same polarity as the toner may be applied to or between the

Nesa electrode and the metal electrode of the reflector

plate, thus preventing the adherence of the toner which would

otherwise result from the electrostatic power.

In the embodiment described just above, it is also

possible, if desired, to coat the surfaces of the electrodes

with a low surface tension material or to dispose the

electrodes remote from the developing liquid in the passage

while coating the surfaces of the electrodes exposed to the

developing liquid with a low surface tension material.

The developing device of the prZn.t i.nvent ion

designed in the manner described above is applicable to

various types of electrophotographic copying apparatus using

the liquid development, and permits the apparatus body to

adopt any suitable arrangement. In the case of Figure 1i

a photosensitive drum 14 carrying thereon a photosensitive

medium comprising a transparent dielectric layer covering a

photosensitive layer is journalled to the apparatus frame

-18- 4 7 9.217

47 1172 line), by means of a shaft 16 (Indicated by a dot-and-dash electrostatic latent and various means for the formation of Below the drum image are arranged peripherally of the drum. electrode 18 14 and closely spaced therefrom is a developing a developing bias of arcuate cross section for applying from the outlet voltage. The developing liquid 2 is supplied 19 and fully into port of the pump 4 through pipes 12 and drum 14 and the the clearance between the photosensitive the developing liquid developing electrode 18. The rest of the end 181. Part is collected in the container 1 through 4 is supplied as of the liquid delivered from the pump 22 into the clearance cleaning liquid through pipes 20, 21, drum 14 and a blade between the top of the photosensitive cleaning flows down cleaner 23. The liquid once used for of the drum 14 at along a groove 24 formed peripherally into the container 1. either end portion thereof and returns a cross bar The cleaning blade 23 is supported by

47 9. 217

Claims (4)

1. Q$471-72 The claims defining the invention are as follows: 1. A developing device using developing liquid to develop an electrostatic latent image formed on the surface of an electrostatic image bearing member, said device compris- ing: a developing liquid storage tank; a developing portion for contacting said electrostatic image bearing member with developing liquid; pumping means for supplying developing liquid from said storage tank to said developing portion; and means for controlling the density of the developing liquid, and having detecting means for detecting the density of the developing liquid, said detecting means including a detecting chamber immersed within the developing liquid within said storage tank, a developing liquid passage formed across said chamber and arranged to pass therethrough part of the flow of developing liquid supplied by said pumping means.
2. 2. A developing device according to claim 1, wherein said means for controlling the density of the developing liquid comprises toner supply means operable in response to said detector means.
3. 3. A developing device according to claim 1, further comprising stirrer means including a stirring impeller whose rotation produces a flow of developing liquid laterally to the shaft of said impeller and directs said flow of the developing liquid so as to dually cross the path of said stirring impel- ler's blades.
4. 4. A developing device according to claim 3, wherein an intake part for said pumping means is provided along the direction said flow of developing liquid produced by said stirrer means.

   A developing device substantially as hereinbefore

   20- 479,217

   50. 471172 described with reference to the accompanying drawings.

   DATED this THIRTIETH day of NOVEMBER, 1976

   CANON FABUSHLIKI H@ISHA

   Patent Attorneys for the Applicant SPRUSON FERGUSON

   21 42179, 217