JPH03212668A - Toner concentration detecting device - Google Patents

Abstract

PURPOSE:To always accurately detect toner concentration by forming the material of a concentration detecting part on a conveyeing side of an acrylic-based polymer in a positively charged toner concentration detecting device. CONSTITUTION:A detection window 5b in the toner concentration detecting device 9 is formed of the acrylic-based polymer. Then, the electrostatic adhesion of the toner is prevented by the electrostatic repulsion with the positively charged toner which occurs because of the positively charging ability of the acrylic-based polymer, and the toner concentration of the positively charged toner is accurately detected. Namely, since the acrylic-based polymer has the positive charging ability is terms of an electrostatic charging system, the electrostatic repulsive force is generated, especially, to the positively charged toner and the positively charged toner is prevented from electrostatically adhering to the detection part. Therefore, the toner concentration is accurately controlled by using the above polymer as the material of the toner concentration detecting window.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for detecting the concentration of positively charged toner in a developing device for an image forming apparatus that uses an electrostatic recording process, such as an electrostatic copying machine or a printer. Regarding equipment.

[Prior Art] In a well-known image forming apparatus that includes a step of attaching toner to a latent image formed on the surface of an image carrier and making it visible, a two-component developer consisting of toner and a magnetic carrier is used. Those using a system developer have been widely used in the past.

In devices that use this kind of developer, only the toner actually contributes to development, and the carrier has nothing to do with it, so as the development process continues, the amount of toner in the developer decreases and the image density decreases. I can't escape it. Therefore, it is necessary to constantly detect the toner concentration and replenish toner when the concentration decreases.

A number of methods have been proposed to detect the amount of toner for this purpose, including optical means that detects changes in the reflectance of the developer due to changes in the amount of toner in the developer, and magnetic means that detects changes in magnetic permeability. It is put into practical use.

By the way, looking at the behavior of the developer in the developing device, a stirring member is generally provided in the developer storage section, and after the toner is supplied, the stirring member stirs the developer and causes it to flow inside the carrier. Normally, the toner is dispersed evenly.

[Problems to be Solved by the Invention] In such a configuration, it is unavoidable that it takes a certain amount of time after the toner is supplied until it is uniformly mixed in the developer. Therefore, even if the above-mentioned toner detection means is used and operates accurately, it is not necessarily easy to always maintain an appropriate amount of toner in a portion that contributes to actual development.

For example, when toner is supplied to the developer storage section from a relatively small opening, if the toner detection means is placed near the opening, it can detect localized excess toner near the opening during supply, and effectively If the toner is placed at a position away from the aperture, the supplied toner will disperse and it will take time for the detection means to detect this, resulting in a situation where there is actually an excess of toner. There is a risk that this may cause deterioration of image quality such as fog.

Although it is theoretically conceivable to arrange multiple detection means in various locations and process the signals from them collectively, such a method would require complicated ancillary mechanisms and would require space and cost. From this point of view, it is easy to understand that it cannot be put to practical use at all.

Furthermore, the opening position for supplying toner to the developer storage section is
If the developer carrying member that conveys the developer to the development position (often formed in the shape of a sleeve) is relatively large and extends in the longitudinal direction, it may be difficult to prevent uneven toner density. It is difficult to correct, and there are problems such as fogging in a part of the width direction and images with uneven density.

The present invention has been made in order to cope with the above-mentioned situation, and in a developing device using a two-component developer,
It is an object of the present invention to provide a toner concentration detection device for a developing device that can accurately detect toner concentration at all times and obtain images without density unevenness or fogging.

[Means and effects for solving the problems] The present invention is characterized by using a two-component developer consisting of a positively charged toner and a magnetic carrier, and developing this developer with a developer carrying member. In a positively charged toner concentration detection device used in a developing device configured to supply toner to a toner position, at least the material on the developing device side in the concentration detection portion is made of an acrylic polymer. Moreover, this acrylic polymer has a weight average molecular weight of 50.000 to 150.0.
00, the value of weight average molecular weight Mw/number average molecular weight Mn is 1.5 to 3.0, Rockwell hardness (M scale) is 70 or more, and water absorption rate is 0.1% to 0.9%. That is.

With this structure, the toner concentration detection part has excellent wear resistance due to developer rubbing and surface stain resistance against toner, and maintains stability of charging characteristics against temperature and humidity due to moderate hydrophobicity. It was discovered that the positively chargeable nature of the acrylic polymer can prevent electrostatic adhesion caused by the toner due to electrostatic repulsion with the positively chargeable toner, and that it is possible to accurately detect the toner concentration of the positively chargeable toner. .

In other words, since the acrylic polymer is positively chargeable in terms of charge series, it produces an electrostatic repulsion force, especially against positively chargeable toner, and prevents positively chargeable toner from electrostatically adhering to the detection part. do not have. Therefore, by using it as a toner concentration detection window material, it becomes possible to accurately control toner concentration.

The acrylic polymer as the material on the developing device side in the toner concentration detection part according to the present invention is a homopolymer or copolymer of acrylic acid ester or methacrylic acid ester, and the monomers constituting these acrylic polymers are Specific examples include the following compounds.

That is, examples thereof include esters of acrylic acid and methacrylic acid with alcohols such as alkyl alcohols, halogenated alkyl alcohols, alkoxyalkyl alcohols, aralkyl alcohols, and alkenyl alcohols. Specific examples of the alcohol constituting the ester include methyl alcohol, ethyl alcohol,
Alkyl alcohols such as propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, dodecyl alcohol, tetradecyl alcohol, and hexadecyl alcohol; halogenated alkyl alcohols that partially halogenate these alkyl alcohols;
Alkoxyalkyl alcohols such as methoxyethyl alcohol, ethoxyethyl alcohol, ethoxyethoxyethyl alcohol, methoxypropyl alcohol, ethoxypropyl alcohol; aralkyl alcohols such as benzyl alcohol, phenylethyl alcohol, phenylpropyl alcohol; alkenyl alcohols such as allyl alcohol, crotonyl alcohol Alcohol is an example.

The above-mentioned acrylic monomers may be used alone or in combination of two or more, and if necessary, one or more of other copolymerizable monomers may be used. Also good. In this case, it is desirable that the acrylic monomer accounts for 25% by weight or more, preferably 50% by weight or more of the total monomers.

Specific examples of other copolymerizable monomers include the following compounds.

That is, styrene and its derivatives, such as methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, polystyrene, hexylstyrene,
Examples include alkylstyrenes such as heptylstyrene and octylstyrene.

These acrylic polymers are synthesized by known methods such as suspension polymerization, emulsion polymerization, and solution polymerization. weight average molecular weight,
The number average molecular weight is measured by GPC (gas permeation chromatography) under the following conditions.

That is, the column was stabilized in a heat chamber at 40°C, and tetrahydrofuran was flowed as a solvent at a flow rate of 1 mi)/min through the column at this temperature, and the sample concentration was adjusted to 0.05 to 1.0% by weight. 50% THF (tetrahydrofuran) sample solution of the system polymer
~200gI! Inject and measure. The molecular weight distribution of the sample was calculated from the relationship between the logarithm value and the count number of a calibration curve prepared using several types of monodisperse polystyrene standard samples. As a standard polystyrene sample for creating a calibration curve,
For example, one manufactured by Pressure Chemical Co., Ltd. or Toyo Tsudani Gyogyo Co., Ltd. with a molecular weight of 6 x 102.2. IX 103
, 4 X 10", 1.75XIO', 5.I
XIO', 1. lX10', 3.9X10', 8
．． 6 x 105, 2 x 106.4.48 x 10'
It is appropriate to use at least 10 standard polystyrene samples. Also, the detector has RI
(refractive index) detector is used.

In addition, as a column, in order to accurately measure the molecular weight range of 103 to 2 x 106, it is recommended to combine multiple commercially available polystyrene gel columns (for example, Watev
μmstivagef500.103.10' manufactured by S company
10'' combination, Showa Denko's 5hodex
KF-80M, KF-802, 803, 804, 80
5 combination, KA-802, 803, 804, 805 combination, or Toyo Soda's TSKgeI! G100
OH, G2000H, G2500H, G3000H.

G4000H, G5000H, G6000H, G700
A combination of 0H and GMH is desirable.

The weight average molecular weight of the acrylic copolymer is 50.0.
00-150,000, preferably 80,000-1
20.000, and the value of weight average molecular weight Mw/number average molecular weight Mn is 1.5 to 3.0, preferably 1.8 to 2.0.
It is 5. If it exceeds this range, moldability as a window member becomes difficult.

Further, Rockwell hardness is measured based on JIS K 7202, and M scale is used for measurement. The desirable Rockwell hardness of the acrylic resin is 70M or more. In addition, the water absorption rate is based on the JIS-7209A method.
Desirable water absorption is 0.1% to 0.9%, more preferably 0.2% to 0.7%.

[Example] Hereinafter, the present invention will be specifically explained in detail using Examples.

Figure 1 is a side sectional view of a developing device suitable for applying the present invention, which extends perpendicularly to the plane of the paper, and includes a toner supply section 1 and a developing device in which carrier is mixed therein. It is equipped with a developer storage section 2 that holds a toner, and inside the toner supply section 1,
A toner conveying member 3 is provided which is operated by a control means (not shown) to supply toner to the developer storage section when the toner concentration in the developer storage section is reduced.

The toner supply section 1 and the developer storage section 2 communicate with each other through a mesh-like toner supply opening 3a, and the toner is supplied from the supply section 1 to the storage section 2 through the opening by the operation of the conveyance member. shall be taken as a thing.

The developer accommodating portion 2 includes a cylindrical fixed magnet roller 7a having a plurality of magnetic poles on its circumferential surface, and a cylindrical fixed magnet roller 7a surrounding the roller.
A developer carrying member 7 consisting of a non-magnetic sleeve 7b that rotates in the direction of the arrow by a drive source (not shown) is provided.
The member 7 approaches the moving image carrier and applies toner to the electrostatic latent image on its surface to visualize the image.

Reference numeral 4.5 is a screw for agitating and transporting the developer, which is disposed substantially parallel to the developer carrying member 7, and the toner supplied from the toner supply section is transferred to the carrier by the transport screw 5. The tube member 5 is conveyed in the X direction as shown in FIG.
Since it extends to point a, it is transported along this direction.

As shown in the figure, the tube member 5a faces upward, and the tube member 4a has the conveying screw 4 installed therein.
Since the toner has reached the vicinity of the inner conveying screw 4, the toner that has been agitated and conveyed by the conveying screw 5 is further conveyed by the conveying screw and returned to the inside of the developing device.

The developer returned to the developing device is transferred to the conveyance screw 4.
travels along the tubular member 4b in which it is placed, and at this time, it falls through the opening 8 formed in the tubular member, reaches the carrier member 7, is conveyed by the rotating sleeve, and is transferred to the image carrier. It adheres to the formed latent image and makes it visible.

As described above, the toner in the developing device is discharged from the conveyance screw 5 and advances. At this time, a space where no developer exists is not formed inside the tubular member, and the toner is conveyed quickly. In addition, it is preferable to make the diameter of the screw 5 as large as possible so that the toner is quickly and uniformly mixed with the carrier in this transport area. Therefore, by arranging the toner concentration detection device 9 at an appropriate location in this area, it is possible to accurately detect and control the toner concentration contained in the developer that actually contributes to development.

FIG. 3 shows an example of a toner concentration detection device disposed in contact with a tubular member 5a having a conveying screw 5 therein. is attached to the sensor 9b, and a portion is attached to the tubular member 5a.
The light is reflected by the internal developer through a detection window 5b made of a transparent material and reaches a sensor 9c.

Therefore, each of the two stages of emitted light is converted into, for example, a voltage, adjusted so that both are equal at a predetermined concentration, and successively compared, and the output from the sensor 9c is determined by the difference between the output from the sensor 9c and that from the sensor 9b. It will be easily understood that the toner conveying member 3 can be activated or deactivated, and the supply of toner can be controlled to be turned on or off.

By the way, when such a configuration is adopted, the inner wall surface of the detection window 5b, which is normally formed of a transparent synthetic resin of an appropriate material, gradually becomes damaged due to surface contamination such as scratches caused by rubbing by the developer, adhesion of toner due to static electricity, etc. In the present invention, the optical detection window is made of polymethyl methacrylate, an acrylic polymer, with a weight average molecular weight of 100.000 and a weight average molecular weight (Mw) of 100.000. ) to the number average molecular weight (Mw),
That is, it is made of a material with Mw/Mn = 1.92, Rockwell hardness of 100M, and water absorption rate of 0.3%.

For the toner concentration detection device of the present invention, the positively chargeable toner is a styrene-2ethylhexyl acrylate-dimethylethyl methacrylate copolymer (monomer composition ratio 7).
5:10:5) 100 parts by weight, monoazo red pigment 5
A red toner was prepared by adding 0.8 wt % of positively chargeable colloidal silica to a red fine powder having an average particle size of 12.0 μm and consisting of 4 parts by weight of low molecular weight polypropylene.

As the magnetic carrier, ferrite particles (average particle diameter 53 m) coated with a mixed resin of polyvinylidene fluoride-polymethyl methacrylate (composition ratio 1:1) were used.

A developer prepared by mixing the above toner and carrier at a weight ratio of 1=9 was processed at low temperature and low humidity (15°C/10%) using a Canon copier NP-5540 modified to be equipped with the toner concentration detection device of the present invention. Normal temperature (22.5℃/60%)
, high temperature (32.5℃/90%) A 5,000 copy test was conducted in each environment, and it was found that in each environment, there were no scratches on the detection window due to developer rubbing, and no surface contamination of the window due to toner adhesion. The toner density was controlled to be constant, and the toner density on the developing sleeve was always constant during copying from the beginning, and clear images without fog could be obtained.

The material of the toner concentration detection window in Example 1 was methyl methacrylate-2-hydroxylethyl methacrylate copolymer (monomer composition ratio 97:3), polymerization average molecular weight 47.000, Mw/Mn=2.5, It was constructed with a Rockwell hardness of 65M and a water absorption rate of 2.5%.

Similar to Example 1, when an image was created using a developer using positively charged red toner, under high temperature and high humidity conditions, the red toner adhered to the detection window, making it impossible to accurately detect the toner concentration. The density (carrier weight relative to toner weight) was significantly reduced, resulting in a very low density and grainy image. This is thought to be due to a decrease in the charging property of the detection window material under high temperature and high humidity conditions due to its water absorption properties.

The material of the toner concentration detection window in Example 1 was polystyrene (weight average molecular weight 75.000, Mw/Mn=0).
．． 4 Rockwell hardness 70M1 water absorption rate 0.1%).

When an image was created using a developer using positively charged red toner as in Example 1, the red toner adhered to the detection window in all environments, and the image density was low and rough as in Comparative Example 1. All I could get was an image.

This seems to be because polystyrene resin has more negative charging characteristics than acrylic resin.

The toner concentration detection window in Example 1 was replaced with methyl acrylate-methyl methacrylate copolymer (monomer composition ratio 20:80), weight average molecular weight 89,000, M
It was constructed from a material with w/Mn=1.7, Rockwell hardness of 95M, and water absorption rate of 0.4%. For such devices,
For the positively chargeable toner, styrene-2 ethylhexyl acrylate copolymer (monomer composition ratio 75:25) 1
0.5 wt % of positively charged colloidal silica is added to blue fine powder with an average particle size of 12.3 pm consisting of 0.00 parts by weight, 4 parts by weight of copper phthalocyanine pigment, 2 parts by weight of quaternary ammonium salt, and 4 parts by weight of low molecular weight polypropylene. was added to obtain a blue toner.

Using the same carrier as in Example 1, a developer with a toner concentration of 5% was prepared, and a Canon copier NP was used in the same manner as in Example 1.
5540 was subjected to a 5,000-sheet copying test under each environment as in Example 1. In each environment, there was no contamination of the window due to toner adhesion, no scratches on the window due to developer rubbing, and the toner density was low. There were no malfunctions of the detection device, the toner concentration on the developing sleeve during copying was always controlled to be constant from the beginning in each environment, and clear images without fog could be obtained.

The toner concentration detection window in Example 1 was made of methyl methacrylate-butyl methacrylate copolymer (monomer composition ratio 90:10), weight average molecular weight 78,000,
Mw/Mn=2.2, Rockwell hardness 85M1
It was constructed from a material with a water absorption rate of 0.3%. For such an apparatus, the positively chargeable toner contains 100 parts by weight of styrene-2-ethylhexyl acrylate (monomer composition ratio 80:20), 2 parts by weight of an azo yellow pigment, and 2 parts by weight of a quaternary ammonium salt.
A green toner was prepared by adding 0.5 wt % of positively chargeable colloidal silica to a green fine powder having an average particle size of 12.5 μm and consisting of 2 parts by weight of copper phthalocyanine pigment and 2 parts by weight of copper phthalocyanine pigment. As the magnetic carrier, ferrite particles coated with silicone resin and having an average particle diameter of 60 pm were used.

A developer with a toner concentration of 6% was prepared using the above-mentioned toner and carrier, and the same procedure as in Example 1 was carried out using a Canon copier NP5540.
As in Example 1, a 5,000-sheet copying test was conducted under each environment. In each environment, the toner concentration on the developing sleeve during copying was controlled to be constant, and clear images without fog could be obtained. Ta.

[Effects of the Invention] As described above, according to the toner concentration detection device of the present invention, the toner concentration detection portion has excellent abrasion resistance due to developer rubbing and surface stain resistance against toner, and has appropriate hydrophobicity. The positive chargeability of the acrylic polymer prevents electrostatic adhesion caused by the toner due to electrostatic repulsion with the positively chargeable toner. Concentration can be detected accurately.

Therefore, since the toner density can be accurately controlled, it is possible to obtain high-quality images.

[Brief explanation of drawings]

FIG. 1 shows a side sectional view of an embodiment of a developing device according to the present invention. FIG. 2 shows an end sectional view of the main part in FIG. 1, and FIG. 3 is a sectional view illustrating the toner detection device.

Claims (2)

[Claims] (1) A two-component developer consisting of a positively charged toner and a magnetic carrier is used, and this developer is stirred and conveyed through a conveyance section.
In the toner concentration detection device used in the conveyance section of the developing device, in which toner is supplied to the development position by a developer carrying member, at least the material on the conveyance side of the concentration detection section is made of an acrylic polymer. Toner concentration detection device. (2) The acrylic polymer has a weight average molecular weight of 50,
000 to 150,000, weight average molecular weight/number average molecular weight 1.5 to 3.0, Rockwell hardness (JIS-
K7202, M scale) 70 or more, water absorption rate (JIS-
7209A method) 0.1 to 0.9%.