JPH0375857B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a developer for developing electrostatic images in electrophotography, electrostatic recording, electrostatic printing, and the like. In electrophotography, a photoreceptor comprising a photoconductive element is provided with a uniform surface charge in the dark, exposed to light to form an electrostatic charge image, and then developed to form a visible image. Generally, methods for developing such electrostatic images are broadly classified into liquid development methods and soft development methods. The liquid development method uses a liquid developer made by dispersing various pigments and dyes as fine particles in an insulating organic liquid, while the dry development method uses carbon black, etc., in a natural or synthetic resin. This is a developing method that uses a mixture of a toner containing a colorant dispersed therein and a carrier such as iron or glass beads. In general, carriers can be divided into insulating carriers and conductive carriers. Oxidized or unoxidized iron powder is used as the conductive carrier. A typical example of an insulating carrier is a carrier in which the surface of carrier core particles made of a magnetic material such as iron, nickel, cobalt, or ferrite is coated with an insulating resin. Dry development methods include the so-called bristle brush method, impression method, and powder cloud method that use a developer containing only the above-mentioned toner as a main component, as well as a mixture of toner and a carrier made of iron powder or glass beads. There are a so-called magnetic brush method and a cascade method which are used as a developer. By these developing methods, electrostatic particles such as charged toner particles contained in the developer adhere to the electrostatic charge image to form a visible image. This visible image is transferred directly onto a photoreceptor or onto another image support such as paper by heat, pressure, solvent vapor, etc., and then fixed. The present invention relates to a developer used in the magnetic brush method and cascade method among the above-mentioned development methods, that is, an electrostatic image developer composed of toner and carrier. Conventionally, fixing involves directly fusing a toner image obtained by development onto a photoconductive photoreceptor or electrostatic recording medium supporting an electrostatic charge image, or by directly fusing a toner image obtained by development. This is carried out by first transferring a toner image from a photoconductive photoreceptor or an electrostatic recording medium onto a transfer sheet such as paper, and then fusing this. The fusing of the toner image takes place either by contact with solvent vapor or by heating.
As a heating method, a non-contact heating method using an electric furnace and a pressure heating method using a heating roller are generally adopted. The pressure heating method using a heating roller performs fixing by passing the toner image surface of the sheet to be fixed while being in pressure contact with the surface of the heating roller whose surface is made of a material that has releasability for the toner. This method is generally called the heated roller fixing method. In this method, the surface of the heating roller and the toner image surface of the fixing sheet come into pressure contact, so the thermal efficiency when fusing the toner image onto the fixing sheet is extremely good, and the fixing can be performed quickly. Therefore, it is extremely effective particularly for transfer type electrophotographic copying machines intended for high-speed copying. However, in this method, the surface of the heating roller and the toner image come into pressure contact in a heated and molten state, so a part of the toner image adheres to the surface of the heating roller and is transferred, causing stains on the next sheet to be fixed. I have something to urge you to do. This is so-called offset development. Therefore, one of the essential requirements in the heat fixing method is to prevent toner from adhering to the surface of the heating roller. Conventionally, in order to prevent toner from adhering to the surface of the heating roller, for example, the surface of the heating roller was made of a material with excellent mold release properties such as fluororesin, and an offset prevention liquid such as silicone oil was also supplied to the surface. The surface of the heating roller is coated with a thin film of liquid. Although this method is extremely effective in preventing offset development, it generates an odor due to heating of the offset prevention liquid and requires a device for supplying the offset prevention liquid. This has the disadvantage that the mechanism of the copying device becomes complex and high precision is required to obtain stable results, making the copying device expensive. However, if the offset prevention liquid is not supplied, toner will adhere to the surface of the fixing roller and offset development will occur, so despite these drawbacks, it is necessary to supply the offset prevention liquid. is the current situation. Japanese Patent Publication No. 52-3304 describes in detail a toner containing an anti-offset agent developed to compensate for these drawbacks. By using a toner containing an anti-offset agent, even when silicone oil is not supplied to the surface of the fixing roller, efficient and good fixing with the heating roller can be performed without generating an offset phenomenon. Therefore, the mechanism of the fixing device can be simplified, and for example, the accuracy, stability, and reliability of high-speed copying machines incorporating such a fixing device can be improved, and the cost can also be reduced. It has the advantage of being possible. However, toner containing an anti-offset agent has poor fluidity and does not exhibit free flow.
When a developer is prepared by mixing a toner containing an anti-offset agent and an uncoated carrier of iron powder, the anti-offset agent present on the surface of the toner particles is removed from the surface of the uncoated carrier during long-term use. The particles migrate to the surface of the carrier and contaminate or adhere to the surface of the carrier, degrading the developer. Moreover, the current situation is that complete non-offset properties cannot generally be obtained simply by containing polypropylene, which is an anti-offset agent. Therefore, in order to improve the non-offset property, it is necessary to contain a resin having a certain degree of non-offset property in the resin itself. That is, it is a toner using a binder made of a resin having a high molecular weight component and polypropylene. On the other hand, toners whose binder is a styrene resin containing a high molecular weight component with a molecular weight of 100,000 or more has very good non-offset properties, but has a high softening point due to the high molecular weight component contained. , on the contrary, the fixing properties are poor. Therefore, in this case, it is necessary to lower the softening point by including a low molecular weight component, and to determine the resin for the binder by considering the balance between the offset generation temperature and the softening point. However, in this case, since a certain amount of low molecular weight components are contained, the durability as a developer deteriorates. That is, the low molecular weight components of the binder resin, together with the polypropylene which is the anti-offset agent, contaminate the surface of the carrier. As a result, in a developer composed of a toner made of a resin containing polypropylene and a low molecular weight component, the triboelectric charging characteristics of the toner become unstable during long-term use, resulting in changes in image density and fogging. Specifically, as the developer is used, polypropylene as an offset inhibitor and a low molecular weight component resin adhere to the surface of the iron powder carrier particles, which increases the electrical resistance of the carrier particles and lowers the bias current. Moreover, the triboelectric charging characteristics become unstable, resulting in a decrease in the density of the formed image and an increase in fog. Therefore, even if the toner itself has good offset resistance and good fixing properties, the durability of these properties is low and it is therefore necessary to replace the developer early. In the end, the cost becomes high. An object of the present invention is to provide a toner that can be fixed well with a heating roller without causing offset development even when a fixing roller that does not supply an offset prevention liquid to the surface of the toner has the following characteristics. To provide an electrostatic image developer with high durability. The present inventors have proposed an electrostatic image developer composed of a carrier and a toner, in which the carrier is made of a resin selected from a styrene-acrylic resin, an epoxy resin, and a butyral resin. The toner is an insulating coated carrier having a volume resistivity of 6.8×10 ¹³ Ωcm or more, and the toner contains a high molecular weight component having a molecular weight of 100,000 or more.
1 to 20 parts by weight of a styrene-acrylic resin, a colorant, and a polypropylene having a softening point of 100 to 160°C, and the polypropylene is 1 to 20 parts by weight per 100 parts by weight of the styrene-acrylic resin in the toner. It has been found that an electrostatic image developer, which is a heating roller fixing toner containing parts by weight, achieves the above object. That is, the developer of the present invention has good fluidity because the toner contains a binder containing a specific high molecular weight component in a specific ratio and polypropylene as an offset inhibitor. Excellent offset resistance can be reliably obtained, and since the binder contains a low molecular weight component, the temperature required for fixing is low and good fixing properties can be obtained. Moreover, even though polypropylene and low molecular weight components are contained in this way, the low molecular weight components and polypropylene are retained because the binder contains a high molecular weight component with a molecular weight of 100,000 or more in a specific ratio. Because the carrier is difficult to separate from the toner, and because the carrier is coated with a specific type of resin and has a volume resistivity above a certain level,
The low molecular weight components contained in the binder and polypropylene are prevented from adhering to the carrier, and as a result, the above-mentioned offset is prevented and at the same time good development is achieved without fogging even during long-term development. A developer with excellent durability can be obtained. Therefore, the developer of the present invention is particularly suitable for high-speed electrophotographic copying machines. In the present invention, the resin for forming the carrier coating is selected from styrene-acrylic resins such as styrene-methyl methacrylate and styrene-butyl methacrylate, epoxy resins, and butyral resins. In order to manufacture the carrier used in the present invention, a coating liquid is prepared by dissolving the above-mentioned resin in a solvent, and this coating liquid is applied to the surface of carrier core particles. For this application, a dipping method, a spraying method, etc. can be used, but a fluidized bed method is particularly preferred. This fluidized bed method uses a pressurized gas flow that rises in a fluidized bed device to raise and suspend the core particles to an equilibrium height, and the coating liquid is removed until the core particles fall again. This is a method in which the coating is applied to each particle by spraying from above, and this is repeated to form a coating film of a desired thickness, and by this method it is possible to apply uniform coating to each particle. Other resins with good compatibility may be mixed and dissolved in the coating liquid. The solvent used in the above may be one that dissolves the resin, such as alcohols such as methanol, ethanol, butanol, and isopropanol; halogenated hydrocarbons such as methylene chloride, dichloroethane, and trichloroethylene; toluene, xylene, etc. Aromatic hydrocarbons such as; ketones such as acetone and methyl ethyl ketone; organic solvents such as tetrahydrofuran and dioxane, or mixed solvents thereof are used. In the above, the nuclear particles preferably have a particle size of 10 to 1000 microns, particularly 20 to 300 microns,
Also, the thickness of the resin coating layer is 0.1 to 10 microns, especially 0.2
~5 microns is preferred. The carrier in the present invention has a volume resistivity of 6.8
It has an insulating property of ×10 ¹³ Ω・cm or more. Here, "volume resistivity" means that 1 g of a sample is placed in a container with a recess of 1 cm ² in area and 1 cm in depth, the inner circular bottom of which is a brass electrode plate, and a brass electrode weighing 1 kg is inserted from above. This is the value measured under the condition that the sample layer was placed on the sample layer. If a carrier having a volume resistivity of less than 6.8×10 ¹³ Ω·cm is used, the resulting developer will have poor durability. Although this carrier is preferably spherical, the effects of the present invention will not be lost even if it is non-spherical. In the developer toner according to the present invention, the resin used as the binder is a styrene-acrylic copolymer. Examples of monomers for the styrene component of this copolymer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, and 2,4-dimethylstyrene. , p-n-butylstyrene, p-tert-butylstyrene, p-n-
hexylstyrene, p-n-octylstyrene,
Examples include p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, etc. . Examples of monomers for the acrylic component include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate,
Methyl methacrylate, ethyl methacrylate,
Propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate , dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and other α-methylene aliphatic monocarboxylic acid esters. These monomers can be used alone or in combination. In particular, a terpolymer consisting of the three components styrene-methyl methacrylate-butyl methacrylate is preferred as the binder. The above styrene-acrylic resin is composed of a low molecular weight component and a high molecular weight component, and contains 10 to 38% by weight of a high molecular component having a molecular weight of 100,000 or more. If the proportion of such high molecular weight components is less than 10% by weight, a high offset generation temperature cannot be obtained and excellent offset resistance cannot be obtained. A styrene-acrylic resin containing such a high molecular weight component can be easily obtained by appropriately selecting polymerization conditions or by forming a crosslinked polymer using a crosslinking agent or the like. The molecular weight in this specification is determined by the gel permeation chromatography method under the following conditions. Tetrahydrofuran was flowed at a flow rate of 1 ml/min at a temperature of 25°C, and the concentration was 0.4.
A sample weight of 8 mg of a g/dl tetrahydrofuran solution is injected and measured. When measuring the molecular weight of a sample, the measurement conditions are such that the molecular weight distribution of the sample falls within a range where the logarithm of the molecular weight and the count number of a calibration curve created using several types of monodisperse polystyrene standard samples are linear. Select. The above measurements were performed using HLC-802UR equipment manufactured by Toyo Soda Co., Ltd.
The column used was TSK-GEL/CMH6. 10% by weight of high molecular weight components with a molecular weight of 100,000 or more
The styrene-acrylic resin containing the above can be produced, for example, as follows. Synthesis example: Partially saponified polyvinyl alcohol "Gohsenol GH-17" in a separable flask with a capacity of 1
(manufactured by Nippon Gosei Co., Ltd.), dissolved in 100 ml of distilled water, added monomer mixture A shown in Table 1 below, suspended and dispersed, and after replacing the gas phase with nitrogen gas, 80°C Raise the temperature to 150 ml and keep at this temperature for 15 hours to polymerize. After that, it was cooled to a temperature of 40℃, and the monomer mixture B shown in Table 1 was added thereto, and the temperature was 40℃.
Continue stirring for 2 hours. Next, partially saponified polyvinyl alcohol “Gohsenol GH-
Separately prepare 100 ml of distilled water containing 0.4 g of ``17'' and add that aqueous solution to the suspension system. Thereafter, the temperature was raised again to 80°C and maintained at this temperature for 8 hours to carry out polymerization, and then the temperature was further raised to 95°C and maintained for 2 hours to complete the polymerization. Thereafter, it is cooled, dehydrated, washed repeatedly, and dried to obtain a resin. This resin has a number average molecular weight Mn
1.1×10 ⁴ , the ratio Mw/Mn of weight average molecular weight Mw to number average molecular weight Mn is 4.5, and the softening point when measured by the ring and ball method specified in JISK2531-1960.
The temperature was 140±2°C.

[Manufacture of carriers]

1 Carrier 1 Prepare a coating solution by dissolving 5 g of styrene-methyl methacrylate resin with an average molecular weight of 150,000 in 300 ml of methyl ethyl ketone, and add 1 kg of sintered iron powder "EFVS" (manufactured by Nippon Iron Powder Co., Ltd.) of 200 to 300 meshes. After putting it in the coating solution and removing the supernatant liquid, it was dried by blowing hot air while stirring in a photographic vat, and then the powder was heat-treated in an oven at a temperature of 100°C for 2 hours,
Thus, a carrier 1 having a resin coating was obtained. The volume resistivity of this carrier 1 was 2.3×10 ⁹ Ω·cm. 2 Carrier 2 20g of epoxy resin and 300ml of methyl ethyl ketone
A coating solution is prepared by dissolving the powder in a fluidized bed device, and sprayed onto 1 kg of spherical steel shot with an average particle size of 100 microns at a fluidized drying temperature of 60°C. 2 in the oven at 100℃
After heat treatment for a period of time, a carrier 2 having a resin coating was obtained. The volume resistivity of this carrier 2 is 10 ¹⁴
It was more than Ω・cm. 3 Carrier 3 A carrier 3 having a resin coating was obtained in the same manner as in the production of carrier 2, except that polyvinyl butyral resin "Eslec B" (manufactured by Sekisui Chemical Co., Ltd.) was used instead of the epoxy resin. The volume resistivity of this carrier 3 was 6.8×10 ¹³ Ω·cm. 4 Carrier 4 Styrene-butyl methacrylate resin with an average molecular weight of 130,000 was used as the coating resin, and iron powder "DSP-135C" (manufactured by Dowa Iron Powder Co., Ltd.) was used.
A carrier 4 having a resin coating was obtained in the same manner as the production of carrier 2. The volume resistivity of this carrier 4 was 10 ¹⁴ Ω·cm or more. [Manufacture of toner] 1 Toner 1 25% by weight of high molecular weight components with a molecular weight of 100,000 or more
Contains styrene-acrylic resin "Eslec"
(manufactured by Sekisui Chemical Co., Ltd.), 3.5 parts by weight of low softening point polypropylene "Viscol 660P" (manufactured by Sanyo Chemical Industries, Ltd., softening point 145°C), and 10 parts by weight of carbon black were mixed in a ball mill. Following the normal toner manufacturing method using each process of pulverization and classification,
Toner 1 with an average particle size of 11.6 microns was obtained. 2 Toner 2 15% by weight of high molecular weight components with a molecular weight of 100,000 or more
Contains 100 parts by weight of styrene-2-ethylhexyl acrylate (softening point 138℃) and low softening point polypropylene "Viscoll 660P" (softening point 145℃)
Using 5 parts by weight and 10 parts by weight of carbon black, the average particle size was 12.9 in the same manner as in the production of toner 1.
Micron toner 2 was obtained. 3 Toner 3 38% by weight of high molecular weight components with a molecular weight of 100,000 or more
Containing 100 parts by weight of styrene-acrylic resin (sample manufactured by Sekisui Chemical Co., Ltd.), 4 parts by weight of low softening point polypropylene "Viscol 550P" (manufactured by Sanyo Chemical Industries, Ltd., softening point 150°C), and 10 parts by weight of carbon black. Toner 3 with an average particle size of 12.9 microns was obtained in the same manner as in the production of Toner 1. Example One of the above carriers 2 to 4 and one of the toners 1 to 3 are mixed in the combination shown in Table 2 in a ratio that gives the toner concentration (weight %) shown in the table, and the total is Three types of electrostatic image developers of the present invention were prepared, and each developer was continuously copied using an electrophotographic copying machine "U-BixW (modified model)" (manufactured by Konishiroku Photo Industries Co., Ltd.) equipped with a heating roller fixing device. A durability test was conducted. The results are shown in Table 2. In Table 2, the term "high molecular weight component" refers to a component having a molecular weight of 100,000 or more in the binder of the toner.

[Table] As can be understood from the above results, the electrostatic image developer of the present invention does not cause fogging even when subjected to a large number of developments, and can achieve good development. It has durability and is free from image stains caused by offset development, making it possible to obtain excellent copied images. Comparative Example 1 8% by weight of high molecular weight components with a molecular weight of 100000 or more
A comparative developer with a toner concentration of 5% by weight was prepared by using Comparative Toner 1 obtained in the same manner as in the production of Toner 1 except that the styrene-acrylic resin contained therein was used as a binder, and Carrier 1 described above. When a durability test similar to the above was conducted, before the number of copies reached 10,000, the staining caused by the offset phenomenon became severe and fogging also occurred, so the experiment was discontinued. Comparative Example 2 A comparative developer with a toner concentration of 5% by weight was made from 200 to 300 mesh iron powder "EFV-" (manufactured by Nippon Iron Powder Co., Ltd.) and the aforementioned Toner 1, and it had the same durability as the example. When a test was conducted, the fixing properties were sufficient, but fogging occurred before the number of copies reached 10,000, so the experiment was discontinued. Comparative Example 3 15% by weight of high molecular weight components with a molecular weight of 100,000 or more
100 parts by weight of styrene-acrylic resin contained;
Comparison Toner 2, which had an average particle size of 12.0 microns, was obtained in the same manner as Toner 1 using 0.05 parts by weight of polypropylene "Viscol 660P" and 10 parts by weight of carbon black, and 5 parts by weight of Toner 2 and 95 parts by weight of Carrier 1. Comparative developer 3 was prepared by mixing and a durability test was conducted in the same manner as in Example 1. However, before the number of copies reached 10,000, the staining caused by the offset phenomenon became severe and the experiment was discontinued. Comparative Example 4 15% by weight of high molecular weight components with a molecular weight of 100000 or more
100 parts by weight of styrene-acrylic resin contained;
30 parts by weight of polypropylene “Viscol 660P”,
Comparative developer 4 was prepared by mixing 5 parts by weight of comparative toner 3 with an average particle size of 12.0 microns obtained in the same manner as toner 1 using 10 parts by weight of carbon black, and 95 parts by weight of carrier 1. When a durability test similar to that in Example 1 was conducted, staining due to the offset phenomenon became severe and fogging occurred before the number of copies reached 10,000, so the experiment was discontinued. Comparative Example 5 15% by weight of high molecular weight components with a molecular weight of 100000 or more
100 parts by weight of styrene-acrylic resin contained;
Comparative Toner 4 with an average particle size of 12.0 microns obtained in the same manner as Toner 1 using 5 parts by weight of polypropylene (softening point 96°C) and 10 parts by weight of carbon black.
Comparative developer 5 was prepared by mixing 5 parts by weight of 5 parts by weight of Carrier 1 with 95 parts by weight of Carrier 1, and a durability test similar to that in Example 1 was conducted. The dirt caused by
In addition, fogging occurred, so the experiment was discontinued. Comparative Example 6 15% by weight of high molecular weight components with a molecular weight of 100,000 or more
100 parts by weight of styrene-acrylic resin contained;
Comparative Toner 5 with an average particle size of 12.0 microns obtained in the same manner as the toner using 5 parts by weight of polypropylene (softening point 170°C) and 10 parts by weight of carbon black.
Comparative developer 6 was prepared by mixing 5 parts by weight of 5 parts by weight of Carrier 1 with 95 parts by weight of Carrier 1, and the same durability test as in Example 1 was conducted. Contamination due to the offset phenomenon caused by the defect became severe, and the experiment was discontinued.

Claims (1)

[Scope of Claims] 1. In an electrostatic image developer composed of a carrier and a toner, the carrier has a core formed by a resin selected from a styrene-acrylic resin, an epoxy resin, and a butyral resin. The toner is an insulating coated carrier coated with particles and having a volume resistivity of 6.8×10 ¹³ Ωcm or more, and the toner contains 10 to 38 high molecular weight components with a molecular weight of 100,000 or more.
1 to 20 parts by weight of a styrene-acrylic resin, a colorant, and a polypropylene having a softening point of 100 to 160°C, and the polypropylene is 1 to 20 parts by weight per 100 parts by weight of the styrene-acrylic resin in the toner. An electrostatic image developer characterized in that it is a heating roller fixing toner containing part by weight.