JPH0619210A - Electrostatic charge image developing carrier and production thereof - Google Patents

Abstract

PURPOSE:To efficiently produce an electrostatic charge image developing carrier capable of forming a high-quality picture uniform in density and free from stains by improving the charge maintainability of the carrier and preventing the deposition of the carrier on a picture. CONSTITUTION:This carrier is coated with at least two kinds of resins. The softening points of the resins are different from each other by >=30 deg.C. The peak of heat of fusion of the blended coating resin by the differenital scanning calorimeter corresponding to the softening point of the high-softening-point resin is controlled to >=30% of the heat of fusion of the blended resin. The coating resin and a nuclide grain are mixed in a dry state, the mixture is heated and melted to coat the grain, and the desired carrier is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing carrier used for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method or the like with a two-component developer, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art A method of visualizing image information through an electrostatic latent image such as an electrophotographic method is currently used in various fields. In the electrophotographic method, an electrostatic latent image is formed on a photosensitive member by a charging and exposing process, the electrostatic latent image is developed with a developer containing toner, and then transferred and fixed to be visualized. The developer used here includes a two-component developer composed of a toner and a carrier and a one-component developer such as a magnetic toner which is used alone as a toner. In the two-component developer, the carrier is a developer. It is widely used at the present time because it has functions such as good controllability because it is divided into functions such as stirring, carrying, and charging and is separated as a developer. In particular,
A developer using a resin-coated carrier has excellent charge controllability, and is relatively easy to improve in environmental dependency and stability over time. Further, as a developing method, a cascade method or the like has been used in the old days, but at present, a magnetic brush method using a magnetic roll as a developer conveying unit is mainly used.

In the magnetic brush method using a two-component developer,
There are problems such as a decrease in image density due to charge deterioration of the developer, a remarkable stain on the background portion, image roughness and carrier consumption due to carrier adhesion to the image, and further uneven image density. The mechanism of carrier attachment to the image is
When the carrier resistance decreases, the induced charge is injected into the image area to attach the carrier, or the upper limit control of the charge amount of the carrier is insufficient, and the charge amount of the carrier after development becomes excessive. It is considered that the carrier adheres to the edge portion.

In recent years, negatively charged organic photoconductors have become widespread, and even in the case of inorganic photoconductors, the reversal development method of recording an electrostatic charge image by using a laser or the like has come to be widely used, not to mention negatively charged toner. Also, there is a high demand for high-quality developer for positively charged toner.

A carrier coated with a fluorine-containing resin has been proposed as a carrier for positively charged toner. However, fluorine-containing resins such as polyvinylidene fluoride have poor adhesion to core particles, and in many cases the charge retention is insufficient after long-term use. In addition, the coating material is detached during use to reduce the electric resistance of the carrier, and carrier adhesion is likely to occur, and black spots and density unevenness are likely to occur due to the detachment coating material. Furthermore, JP-A-54-110
Japanese Patent No. 839 proposes to use an adhesion-imparting resin together for the purpose of improving the adhesion of the negatively chargeable resin to the core particles, but it was not always possible to obtain a sufficient effect.

Further, the fluorine-containing resin generally has a strong negative chargeability, and control of the chargeability is important from the viewpoint of maintaining image quality. Therefore, it is necessary to use the charge control resin in combination, but it is not easy to select the resin and the charging effect tends to vary depending on the process conditions at the time of coating.

[0007]

Therefore, the present invention is intended to solve the above problems and provide a carrier for developing an electrostatic image having the following features and a method for producing the same. The chargeability of the carrier is controlled to prevent the image density from being reduced due to overcharging and the background stain due to charge decay, to prevent the carrier from adhering to ensure stable image quality and to suppress the consumption of the carrier. Application, it can be applied to high-quality developers for reversal development on inorganic photoconductors, improving image quality maintenance due to changes in charging properties due to environmental changes, etc., and efficiently developing carriers for electrostatic image development. To manufacture.

[0008]

The present invention comprises at least two aspects.
In a carrier formed by coating different kinds of resins, the softening points of the resins differ by 30 ° C. or more, and the melting heat peak corresponding to the softening point of the high temperature side resin by the differential scanning calorimeter of the coated resin after the blending is blended by the blending. A carrier for electrostatic charge image development, in which a coating resin having a heat of fusion of 30% or more of the resin and core particles are mixed in a dry state, and heated and melted to coat the resin, and a method for producing the carrier.

[0009]

FUNCTION It is important in the design of the carrier to coat the magnetic core particles with two kinds of resins having different charging properties to obtain desired charging properties and film strength. Then, in order to exert its performance, the mixed state or compatible state of two kinds of resins is important, and there is also a proposal of a carrier for developing an electrostatic charge image which defines good compatibility. However, from the viewpoint of controlling the charging property, it has been found for the first time by the study of the present inventors that the compatibility of the two kinds of coating resins is not good from the viewpoint of charge control. did. That is, it is particularly remarkable when the chargeability of the carrier depends on the crystallinity of the resin such as a fluororesin, and the chargeability or the charge retention property may be significantly lowered due to the inhibition of the crystallinity. As a result of the study, it was found that it is effective that the two types of resins are not necessarily compatible with each other and exist separately on the surface of the carrier in order to obtain a desired chargeability.
In this case, the two kinds of coating resins form a microscopic sea-island dispersion on the carrier. In order to form such a coating state, it is important to select resins having greatly different compatibility, and the process conditions at the time of coating influence.

In particular, in the method of mixing the coating resin and the core particles in a dry state and then heating to melt the coating resin to coat the core particles, the difference in softening point between the two resins is Is a major factor for forming incompatibility and has a difference in softening point of 30 ° C. or higher, an incompatible state can be obtained relatively easily. At this time, if the carrier after coating is subjected to a differential scanning calorimeter, the melting heat peak corresponding to the softening point of the high temperature side resin can be observed according to the compatible state, and this is used as an index for process conditions and material selection. The combination of can be optimized. In particular, when the high temperature softening point resin is a fluorine-containing resin, the heat of fusion corresponding to the high temperature side softening point in the carrier coated state decreases as the compatibility progresses, as compared with the raw material resin,
Correspondingly, the chargeability and charge maintainability are also affected.

Therefore, in the present invention, at least two kinds of coating resins are used, and the softening points of the respective resins are different by 30 ° C. or more, and the softening point of the resin on the high temperature side by the differential scanning calorimeter of the coating resin after the blending is used. By using a coating resin whose corresponding heat of fusion peak is 30% or more of the heat of fusion of the compounded resin, the charge retention of the carrier is improved, the carrier is prevented from adhering to the image, and uneven density and scumming are prevented. It is now possible to provide excellent image quality. As a result, it becomes possible to significantly reduce the consumption of the carrier. Furthermore, by mixing the coating resin and the core particles in a dry state in advance and then melt coating, it is possible to efficiently manufacture the carrier. Became.

Examples of the fluorine-containing resin used in the present invention include copolymers of vinyl-based fluorine-containing monomers such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene and trifluoroethylene. Further, as the combination resin, styrenes such as styrene, chlorostyrene, and methylstyrene; methyl methacrylate, methyl acrylate, propyl acrylate, lauryl acrylate, methacrylic acid, acrylic acid, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl Α-Methylene aliphatic monocarboxylic acids such as methacrylate; nitrogen-containing acrylics such as dimethylaminoethyl methacrylate; nitric acid such as acrylonitrile and methacrylonitrile. Lil acids; 2─ vinylpyridine,
4-Vinyl pyridines such as vinyl pyridine; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene; and homopolymers or copolymers of silicons such as methyl silicon and methyl phenyl silicon. In addition, polyesters containing bisphenol, glycol, etc. can also be used. It is also possible to mix two or more of the above-mentioned combination resins to prepare a coating composition mainly for negatively charged toner.
In that case as well, optimization of the compatibility of the two kinds of coating resins is an important issue as in the past, and optimization by the peak separation behavior in the differential scanning calorimeter is required. The amount of the coating resin compounded is about 0.2 to 10% by weight, preferably 0.5 to 10% by weight based on the total amount of the fluorine-containing resin and the combined resin with respect to the carrier.
A range of 3% by weight is suitable.

The core particles used in the present invention may include ordinary iron powder, ferrite, magnetite granules and the like, and the average particle diameter thereof is usually about 30 to 200 μm. To manufacture the carrier of the present invention,
A heating type kneader, a heating type Henschel mixer, a UM mixer or the like can be used, and a heating type fluidized rolling bed, a heating type kiln or the like can be used depending on the compounding ratio such as the amount of resin.

The carrier of the present invention is mixed with a toner to prepare a toner.
Used as a component developer. The toner is a binder resin in which a colorant or the like is dispersed. Examples of the binder resin used in the toner include styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate, ethyl acrylate. , N-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate,
Α-methylene aliphatic monocarboxylic acid esters such as lauryl methacrylate and 2-ethylhexyl methacrylate;
Vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl pyridines such as 2-vinyl pyridine and 4-vinyl pyridine; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc. Vinyl ketones; polymers of monomers such as unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene and halogenides thereof, halogenated unsaturated hydrocarbons such as chloroprene, or
Copolymers obtained by combining two or more of these monomers, and mixtures thereof, and further rosin-modified phenol formalin resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin, etc. Examples of the non-vinyl-condensed resin, or a mixture of these with the vinyl-based resin.

Examples of the colorant used in the toner include carbon black, nigrosine dye, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue, and mixtures thereof. As the toner component other than the colorant, a salicylic acid metal salt, a metal-containing azo compound, nigrosine, a charge control agent such as quaternary ammonium salt, low molecular weight polypropylene, low molecular weight polyethylene,
Known components such as an anti-offset agent such as wax and a fluidity improver can be added, and among them, a low molecular weight polypropylene having a weight average molecular weight of 500 to 5000 is particularly effective. In addition, you may contain a magnetic substance fine powder as needed. The toner is manufactured by blending the above toner materials and mixing them using a Banbury mixer, a kneader coder, a CM mixer, an extruder, etc., melt kneading, and pulverizing and classifying to obtain an average particle size of about 30 μm or less, particularly It is preferable that the particle size is 3 to 20 μm.
Furthermore, silica, titania, fluidizing agents such as alumina, polystyrene fine particles, polymethylmethacrylate fine particles,
External additives such as cleaning aids such as polyvinylidene fluoride fine particles or transfer aids can be used, and among them, hydrophobic silica having a primary particle size of 5 to 30 nm is particularly effective.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the present invention is in no way limited by these examples. Example 1 100 parts by weight of Cu—Zn ferrite core particles having an average particle size of 80 μm were added to K manufactured by Pen Walt Co., Ltd.
YNAR7201 (polyvinylidene fluoride: softening point 12
4 ° C.) 1 part by weight and styrene-n-butyl methacrylate-MMA copolymer (softening point 85 ° C.) manufactured by Soken Chemical Industry Co., Ltd.
Mix 5 parts by weight, mix for 5 minutes with a 1 L small kneader,
The heat medium temperature is set to 200 ° C, and the blade peripheral speed is 10 cm / s.
After stirring and kneading for 40 minutes at ec, the heater was turned off, and the mixture was cooled for 50 minutes while stirring. Then, sieving was performed with a 177 μm sieve to obtain a carrier. The amount of heat of fusion of the fluororesin of the above-mentioned coated carrier is determined by Shimadzu Thermal Analyzer DS.
When measured at a temperature rising rate of 10 ° C./min using C50, it was 13 J / g, which was 46% of the raw material fluororesin. The toner is 86% by weight of a binder resin (styrene-n-butyl methacrylate), 8% by weight of carbon black (BPL made by Cabot), 2% by weight of a charge control agent (Bontron N04 made by Orient Chemical Co.), and polypropylene wax. (Sanyo Kasei 660P) 4% by weight was used to obtain a toner having an average particle size of 10 μm by a kneading and pulverizing method. Then, the above-mentioned toner and carrier were mixed to obtain a developer so that the toner concentration becomes 4%. An image quality maintenance test was performed on this developer using a modified FX5017 machine manufactured by Fuji Xerox. As a result, the developer had no problem in the image after copying 100,000 sheets, and the image quality maintaining property was good. In addition, the consumption of the carrier was also small. further,
Under high temperature and high humidity (30 ℃, 80% RH), low temperature and low humidity (10
When an image maintaining property test was carried out on each of 50,000 sheets under a condition of 20 ° C. and 20% RH, the image had no problem and the image quality maintaining property under each environment was also good.

(Example 2) 100 parts by weight of the core particles of Example 1 were used, and KYNAR7201 manufactured by Penwalt Co. was used.
(Polyvinylidene fluoride: softening point 124 ° C.) 1 part by weight and Toray Dow Corning Methylphenyl silicone resin (softening point 90 ° C.) 0.3 part by weight were mixed and mixed with a 1 L small kneader for 5 minutes, and a heat medium was added. Set the temperature to 200 ℃,
After stirring and kneading at a blade peripheral speed of 10 cm / sec for 40 minutes, the heater was turned off, and cooling was performed for 50 minutes while stirring.
Then, sieving was performed with a 177 μm sieve to obtain a carrier. The heat of fusion of the coated fluororesin in a carrier coat state was 14 J / g, which was 50% of the heat of fusion of the raw fluororesin. The same toner as in Example 1 was used, and an image quality maintenance test was conducted in the same manner as in Example 1.
The initial image quality was good, and the image after copying 150,000 sheets had no problem, and the image quality maintaining property was also good. In addition, the consumption of the carrier was also small. Furthermore, high temperature and high humidity (30
Low temperature, low humidity (10 ℃, 20% RH) under ℃, 80% RH)
When an image sustainability test was performed on 50,000 sheets under each of the conditions below, there were no problems with the images, and the image quality sustainability under each environment was also good.

(Comparative Example) The same raw materials as in Example 1 were blended,
After mixing for 5 minutes with a 1 L small kneader, setting the heat medium temperature at 220 ° C., stirring and kneading for 30 minutes at a blade peripheral speed of 25 cm / sec, and continuing stirring for 20 minutes at the ultimate temperature, then,
The heater was turned off, and the mixture was cooled for 50 minutes while stirring. Then, sieving was performed with a 177 μm sieve to obtain a carrier. The amount of heat of fusion of the coated fluororesin in the carrier state is 8
It was J / g, which was 28% of the heat of fusion of the raw material fluororesin. When the same toner as that in Example 1 was used and an image quality maintenance test was conducted in the same manner as in Example 1, the initial image quality was good, but the roughness of the image due to carrier adhesion was noticeable after copying about 2,000 sheets. Initially, after the copying of about 20,000 sheets, the unevenness of the image density occurred due to the decrease of the developer, so the test was stopped. Also, high temperature and high humidity (30 ℃, 80%
When an image sustainability test was performed under RH), image roughness and background stain were generated from 2,000 sheets.

[0019]

According to the present invention, by adopting the above-mentioned constitution, the charge maintaining property of the carrier can be improved,
The carrier is prevented from adhering to the image, and excellent image quality without density unevenness or background stain can be obtained. Further, it becomes possible to significantly reduce the consumption amount of the carrier, and further, by mixing the coating resin and the core particles in a dry state in advance and then melt coating, it is possible to efficiently manufacture the carrier. became.

Claims (2)

[Claims] 1. A carrier formed by coating at least two kinds of resins, each resin having a different softening point of 30 ° C. or more, and corresponding to the softening point of the resin on the high temperature side by a differential scanning calorimeter of the coated resin after the blending. A carrier for developing an electrostatic charge image, comprising a resin having a heat of fusion peak of 30% or more of the heat of fusion of the compounded resin. 2. A method for producing a carrier for developing an electrostatic charge image, comprising mixing a coating resin and core particles in a dry state, heating and melting the resin to coat the resin, and at least two kinds of resins are used as the coating resin. The softening points of the resins differ by 30 ° C. or more, and the melting heat peak corresponding to the softening point of the high temperature side resin by the differential scanning calorimeter of the coated resin after blending is 30% or more of the melting heat amount of the blended resin. A method for producing a carrier for developing an electrostatic charge image, which comprises using a resin.