JPH04235565A - Magnetic developer for heat roll fixing - Google Patents

Abstract

PURPOSE:To obtain a magnetic developer used for heat roll fixing and providing images of high quality having high image concentration and excellent resolution, while preventing fogging. CONSTITUTION:In a magnetic developer used for heat roll fixing and formed out of a magnetic toner containing a binding resin, magnetic powder, a charge controlling agent and a mold releasing agent, being mixed with a magnetic carrier, powder of a polymer such as sthyrene, acryl, etc., of grain size 0.1 to 1.0mum which polymerizes in the presence of an emulsion of 10ppm or less (not including zero) is added by 0.05 to 1.0 parts by weight to 100 parts by weight of the magnetic toner and attached to the surface of the magnetic toner.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention is a method for mixing a magnetic carrier and a magnetic toner, which is used when developing an electrostatic image formed on the surface of an image carrier by a magnetic brush method. The present invention relates to a magnetic developer for hot roll fixing, and particularly to a magnetic developer for hot roll fixing that has been improved so as to improve image quality. 2. Description of the Related Art A magnetic brush method is generally used to develop an electrostatic charge image formed on the surface of an image carrier. The developer used in magnetic brush development is often a two-component developer in which a magnetic carrier and a non-magnetic toner are mixed. On the other hand, there is also a method of using a one-component developer consisting of resin and magnetic powder as the developer. In the former method using a two-component developer, although an image with good image density and resolution can be obtained, there is a problem in that the reproducibility of halftones is poor. On the other hand, the latter method using a one-component developer has problems such as charge aggregation development of the toner due to an increase in the amount of toner charge, and insufficient development due to insufficient toner on the sleeve. As a means to solve these problems, a developer in which a magnetic carrier and a magnetic toner are mixed has been proposed, for example, as described in Japanese Patent Publication No. 2-31383. It is said to have the advantages of both component-based developers. [0004]Problems to be Solved by the Invention: By using a magnetic developer formed by mixing a magnetic carrier and a magnetic toner as described above, relatively high quality images can be obtained, but as the number of copies increases, A slight decrease in image quality will occur. That is, there is a problem in that the reduction in the triboelectric charging ability of the magnetic toner causes a reduction in image density or background fog, resulting in a reduction in image quality. As a countermeasure to this problem, it may be possible to increase the amount of charge control agent contained in the magnetic toner, but if the amount of charge control agent is too large, the fixing properties of the toner image after being transferred to recording paper etc. will be impaired. It's inconvenient. [0005] Furthermore, a method has been proposed in which a fine polymer powder obtained by emulsion polymerization without an emulsifier (so-called soap-free polymerization) is adhered to the surface of a toner as described in Japanese Patent Publication No. 2-3172. However, although the addition of the above-mentioned fine powder is effective in preventing so-called toner filming, in which toner adheres to the surface of the image carrier, it is not necessarily recognized to be effective as a means for preventing the above-mentioned reduction in image density or background fog. do not have. On the other hand, in recent years, the requirements for magnetic developers for hot roll fixing have become increasingly strict, and higher image quality is required, and it is necessary to further improve image quality. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic developer for hot roll fixing that can solve the problems existing in the prior art described above, prevent background fog, and provide high-quality images. Means for Solving the Problems In order to achieve the above object, in the present invention, a magnetic toner containing a binder resin, magnetic powder, a charge control agent and a mold release agent, and a magnetic carrier are used. In the mixed magnetic developer for hot roll fixing, 10p. p. m. Polymerizes in the presence of the following emulsifiers (excluding 0) and has a particle size of 0.
0.05 to 1.0 μm of fine powder of a polymer such as styrene or acrylic having a diameter of 1 to 1.0 μm is added to 100 parts by weight of magnetic toner.
A technical method of adding and adhering parts by weight was adopted. In the present invention, if the particle size of the fine polymer powder to be added and adhered to the surface of the magnetic toner is less than 0.1 μm, no effect of preventing background fog can be expected even if it is applied to the surface of the magnetic toner; If the particle size exceeds 1.0 μm, it is disadvantageous because it cannot be attached to the surface of the magnetic toner. Further, the above-mentioned fine powder is added in an amount of 0.05 to 1.0 parts by weight per 100 parts by weight of the magnetic toner.
If the amount is less than 0.05 parts by weight, no effect of preventing background fogging can be expected, while if it exceeds 1.0 parts by weight, excessive free fine powder will be present, which will deteriorate the charging stability of the magnetic toner, which is disadvantageous. Next, as the magnetic material powder to be contained in the magnetic toner of the present invention, Fe3 O4, Fe
2 O3 , γ・Fe2 O3 , nMO・Fe2 O
3 (However, M is 1 of metal such as Ni, Cu, Mn, Zn, etc.
It is possible to use one or more kinds of iron oxide-based magnetic material powders (n=5 to 6). Among the above materials, Fe is preferred in terms of magnetic properties and hue.
3 O4 is preferred. The magnetic material powder preferably has an average particle diameter of about 0.1 to 3 μm in order to be uniformly dispersed and contained in the magnetic toner. Next, if the content of the magnetic material powder is less than 10% by weight, although the fixing property is improved, the magnetic force of the magnetic toner is reduced, so that it separates from the surface of the developing roll in the developing area, causing background fog. In addition to staining the image,
This is inconvenient because it causes toner scattering. On the other hand, if the above content exceeds 70% by weight, the adsorption force to the surface of the developing roll becomes large, which prevents smooth transfer to the image carrier side in the developing area, reduces developing performance, and inhibits fixing performance in the subsequent stage. It is not desirable because As the binder resin in the present invention, known toner resins can be used, including styrenes, vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, methacrylonitrile, and acrylamide. A homopolymer obtained by polymerizing monomers such as , vinyl ethers, and N-vinyl compounds, a copolymer obtained by copolymerizing a combination of two or more of these monomers, or a mixture thereof can be used. In addition, rosin-modified phenol-formalin resin, oil-modified epoxy resin,
Non-vinyl resins such as non-vinyl thermoplastic resins such as cellulose resins and polyether resins, or mixtures of these and vinyl resins as described above can also be used. In addition, considering offset prevention and fixing performance, Mw/Mn≧2.0
, Mw=50,000 to 300,000, and Mn=5,000 to 50,000. In particular, in the case of a contact heat fixing method using a heated roll, styrene resin or polyester resin is preferable. In order to improve the mold releasability against hot rolls, it is effective to add fatty acid metal salts, low molecular weight polyolefins, and natural or synthetic paraffins. The amount of these mold release agents added is preferably in the range of 0.5 to 10% by weight. If the amount is less than 0.5% by weight, the anti-offset effect will be small, while if it is more than 10% by weight, the fixing performance will deteriorate, which is disadvantageous. These resins can be arbitrarily selected and mixed as desired, but in order not to reduce the fluidity when used as a magnetic toner, it is necessary to use resins with a glass transition point exceeding 40°C or resins. Mixtures are effectively used. [0014] In the magnetic toner of the present invention, various materials such as a coloring agent, a charge control agent, etc. can be used in addition to the above-mentioned binder resin, if necessary. Examples of colorants include carbon black, aniline blue, calco oil blue, chrome yellow, quinoline yellow, DuPont oil red, malachite green oxalate, lamp black,
Pigments or dyes such as rose bengal and nigrosine dyes can be used. As the charge control agent, for example, fatty acid-modified nigrosine dyes, triphenylmethane dyes, metal-containing azo dyes, etc. can be used. Further, the magnetic toner of the present invention may contain inorganic fine powders such as hydrophobic silica, alumina, titanium dioxide, etc., resin fine powders such as polytetrafluoroethylene and polystyrene, etc., if necessary. The amounts of the various materials other than the above-mentioned magnetic material powder and binder resin may be determined depending on the electrical properties required of the magnetic toner, but generally speaking, in order to ensure fixing properties, It is desirable that the content be 5% by weight or less. The magnetic toner of the present invention can be produced by a known method such as a pulverization method, a spray drying method, or a suspension polymerization method. The average particle size is adjusted to . The magnetic developer for hot roll fixing of the present invention is prepared by mixing a magnetic carrier and a magnetic toner, and the mixing ratio (toner concentration) of the magnetic toner is 10 to 90% by weight.
It is desirable to do so. When the toner concentration exceeds 90% by weight, the magnetic toner tends to scatter and the amount of spent toner increases, while when the toner concentration is less than 10% by weight,
The image becomes less sharp, and dust and blur appear. The toner concentration is determined as appropriate depending on the development conditions, etc., but the preferable range is 20 to 80% by weight, and the more preferable range is 30% by weight.
~70% by weight. As the magnetic carrier used in the present invention, known carriers can be used, but from the viewpoint of image quality, magnetite and soft ferrite (Ni-Zn series, Mg-Zn series, Cu-
A carrier containing iron oxide (Zn-based, Ba-Ni-Zn-based, etc.) is preferred. Next, the particle size of the magnetic carrier is
Same as normal two-component developer, average particle size is 20-120μ
m, and the saturation magnetization σs is preferably adjusted to 50 to 70 emu/g. In the present invention, the particle size of the magnetic toner is a value measured using a Coulter Counter Model TA-II (manufactured by Coulter Electronics Co., Ltd.), and the magnetic properties of the magnetic carrier are measured using a vibrating sample magnetometer (VSM manufactured by Toei Kogyo Co., Ltd.). −
III) in a magnetic field of up to 5 kOe. [Example] Styrene-n-butyl methacrylate copolymer
40 parts by weight (Mw=120,000, Mn=1
10,000) Magnetite
55 parts by weight (EPT500 manufactured by Toda Kogyo) Polypropylene
3 parts by weight (Viscol 550P manufactured by Sanyo Chemical) Charge control agent
2 parts by weight
(Orient Chemical Bontron E81) 0
[022] Dry mix the above formulation and use a kneader for 20
The mixture was heated and kneaded at a temperature of 0°C. The resulting mixture was cooled and solidified, and then ground into particles of 20 μm or less using a jet mill. Next, this pulverized powder was introduced into a hot air stream at 120° C. for heat treatment, and then classified using a zigzag classifier to obtain a magnetic toner having a volume average particle diameter of 10 μm. Next, PMM was added to 100 parts by weight of the magnetic toner.
A (polymethyl methacrylate, MP180 manufactured by Soken Chemical Co., Ltd.
1. Particle size 0.35-0.5 μm, molecular weight Mw = 250,000-
500,000) in the ratio shown in Table 1 and mixed in a Henschel mixer to adhere PMMA fine powder to the surface of the magnetic toner to obtain negatively charged magnetic toner A. On the other hand, as a comparative example, instead of the PMMA fine powder in the magnetic toner A, a PMMA fine powder MP1000 manufactured by Soken Chemical Co., Ltd. was attached to form a negatively charged magnetic toner a. Note that while the PMMA in the magnetic toner A is obtained by emulsion polymerization with an emulsifier, the PMMA in the magnetic toner a is obtained by emulsion polymerization without an emulsifier, that is, soap-free. [Table 1] 40 parts by weight of each of the above magnetic toners A and a were mixed with a ferrite carrier (KBN-100 manufactured by Hitachi Metals, particle size distribution 74 to 105 μm) to prepare a magnetic developer for hot roll fixing. Table 1 also shows the results of evaluating the produced, developed and fixed images. The developing conditions and fixing conditions are as follows. That is, the developing device is equipped with a cylindrical permanent magnet with 8-pole symmetrical magnetization inside a sleeve made of SUS304 with an outer diameter of 31 mm, and a magnet roll with a magnetic flux density of 650 G on the sleeve. The electrostatic latent image (surface potential -600 to -400V) on the OPC photoreceptor was developed in reverse. The distance between the photoconductor and the sleeve was 0.4 mm, the toner regulation thickness was 0.35 mm, and the sleeve was rotated at 200 rpm in the same direction as the photoconductor in the developing section. p. m. Rotate the permanent magnet at 900 rpm in the opposite direction to the sleeve. p. m. I rotated it. The developed toner image was corona-transferred onto plain paper and fixed with a hot roll. Fixing is performed using a heating roll whose surface is coated with PFA resin and a pressure roll made of silicone rubber, at a fixing temperature of 180°C and a fixing pressure of 1 linear pressure.
．． It was carried out at 0 kg/cm. As is clear from Table 1, No. In No. 7, background fogging occurred despite the addition of PMMA, and the image quality deteriorated. On the other hand, No. 1 in the present invention. In case No. 4, no ground fog was observed at all, and high-quality images were obtained. Also No. In No. 1, due to the lack of PMMA adhesion, the occurrence of background fog was clearly observed by visual evaluation. On the other hand, No.
In No. 6, since the amount of PMMA added was too large, PMMA particles were scattered from the developing area, contaminating the inside of the machine, and a decrease in image density was also observed. Next, in place of the charge control agent having a negative charge characteristic in the magnetic toners A and a, oil black BY manufactured by Orient Chemical Co., Ltd. having a positive charge characteristic was blended, and after producing a magnetic toner in the same manner as above, a PMMA fine powder was added. As a powder, MP2701S manufactured by Soken Chemical Co., Ltd. (made by emulsifier emulsion polymerization, the above-mentioned M
Fine powder (same as P1801) was added and deposited to obtain a positively charged magnetic toner B. As a comparative example, an emulsifier-free polymer product MP2701 was added and deposited to create positively charged magnetic toner b.
And so. Table 2 is a table showing the amount of PMMA added and the image evaluation results for the positively charged magnetic toners B and b. In addition, under the developing conditions in this case, the OPC photoreceptor (
The process was the same as in the previous example except that regular development was performed on the electrostatic latent image on the negatively chargeable surface. [0031] [Table 2] [0032] As is clear from Table 2, No. 1 using magnetic toner B of the present invention. It was confirmed that the samples No. 9 to No. 12 were free from background fog and could provide high-quality images. Effects of the Invention Since the present invention has the configuration and operation as described above, it has the effect that background fog can be prevented and high quality images with high image density and excellent resolution can be obtained. There is.

Claims (1)

[Claims] 1. A magnetic developer for hot roll fixing comprising a mixture of a magnetic toner containing a binder resin, magnetic powder, a charge control agent, and a release agent, and a magnetic carrier, in which 10p. p. m. Below (however, 0 is not included)
is polymerized in the presence of an emulsifier, and has a particle size of 0.1 to 1.
．． A magnetic developer for hot roll fixing, characterized in that 0.05 to 1.0 parts by weight of 0 μm polymer fine powder such as styrene or acrylic is added and adhered to 100 parts by weight of magnetic toner.