JP2501885B2 - Method for producing coating resin for carrier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for producing a coating resin for a carrier used for a developer such as electrophotography and electrostatic printing.
More specifically, the present invention relates to a method for producing a coating resin for a carrier, which has extremely improved charge imparting action and durability.

(Prior Art and its Problems) In the electrophotographic method and the like, the two-component developing method is suitable for color image formation because a relatively stable and high-quality image can be obtained and it is not necessary to contain a magnetic material in the toner. It is often used because of its compatibility. Further, in order to always perform stable development, it is necessary that the toner and the carrier are uniformly stirred in the developing device and sufficiently frictionally charged, and the charged toner is consumed as the development is repeated. A new amount of toner corresponding to the above condition is replenished, and the mixing and stirring with the carrier are repeated. Therefore, the carrier in the developing device needs to maintain a constant charge imparting action without deterioration, and needs to be rapidly and uniformly stirred with the replenished toner, which requires excellent fluidity and durability. .

On the other hand, in recent years, the electrophotographic method has come to be used in various applications such as copying and high-speed printers, and a toner having a positive charging property is required depending on a photoconductor used or a developing method. Conversely speaking, there is a demand for a carrier which itself has a good negative charging property for positively charging the toner.

However, it has not been possible to sufficiently positively charge the toner even with iron-based carriers and other carriers that are used more often than before. Therefore, it has been attempted to coat a resin component having a strong negative charge property such as tetrafluoroethylene, but since the film-forming property and the durability are poor and the coating layer becomes non-uniform, it is still low-charge toner or uncharged toner. Toner or the like is generated to cause image fog.

Further, JP-A-61-51158 and JP-A-61-51159 propose a resin-coated carrier coated with a mixture of a maleic acid-based polymer and a styrene-based or acrylic-based polymer. However, since the maleic acid-based polymer and the styrene or acrylic polymer have low compatibility, and the solubility in the solvent during coating is different, the resin coating layer of the carrier formed after coating is likely to undergo phase separation and has a uniform composition. Not only is it difficult to form the coating layer, but also the adhesion between the coating layer and the core material is poor, and satisfactory results have not yet been obtained in terms of charging stability and durability.

Furthermore, it is composed of a copolymer of a monomer having a polar group and an oil-soluble monomer having an unsaturated bond, the polar group having a negative polarity is uniformly dispersed, and the adhesiveness to the core material is excellent. It is possible to coat the polar group-containing polymer having a uniform monomer composition alone, but in reality, a single polymer having suitable molecular weight characteristics as a coating resin, sufficient durability and stable charge imparting characteristics. It was difficult to obtain a coalesced product, and even if it could be obtained, it was difficult to produce a polymer with severe condition setting and stable performance with good reproducibility.

The present invention has been made in view of the above-mentioned points, in which an anionic negatively charged polar group is uniformly and uniformly present in the resin to give a stable charge-imparting action, and at the same time, to improve the adhesion and the formation with the core material. An object of the present invention is to provide a manufacturing method capable of stably and stably supplying a coating resin having excellent film properties.

(Means for Solving Problems) At least one oil-soluble monomer selected from the group consisting of vinyl aromatic hydrocarbon monomers and (meth) acrylic acid esters, sulfonic acid, phosphoric acid, or At least one water-soluble monomer having a carboxylic acid type anionic group, dispersion-polymerized in a mixed solvent of water and a water-miscible organic solvent and in the presence of a dispersion stabilizer, water-soluble monomer A high-quality coating resin can be obtained by recovering a copolymer of a vinyl ester and an oil-soluble monomer in the form of particles, and by coating this copolymer, the problem of the above-mentioned carrier for positively charged toner can be obtained. The points are solved and the object of the present invention is achieved.

(Function) In the present invention, one of the vinyl aromatic hydrocarbon monomer constituting the copolymer and the oil-soluble monomer composed of (meth) acrylic acid ester is a component that imparts film-forming property and durability. On the other hand, the water-soluble monomer having a sulfonic acid, carboxylic acid, or phosphoric acid type anionic group is a component responsible for the charge imparting property. Since the polymer is used alone for coating, the resin solution obtained by dissolving in a solvent does not undergo phase separation and becomes a resin solution having a uniform concentration, so that the coating layer after coating has a uniform film thickness. The surface property can be obtained. Further, since the anionic group exhibiting a negative charging property is dispersed in the copolymer, it exhibits a good negative charging property, and the toner can be effectively positively charged.

As a method for producing the above-mentioned polymer, a mixed medium of water and a water-miscible organic solvent is used as a polymerization medium, and both the oil-soluble monomer and the water-soluble monomer are dissolved. ,
It is preferable to use dispersion polymerization in which a dispersion stabilizer is allowed to coexist. According to this dispersion polymerization, a copolymer having a uniform composition containing an oil-soluble monomer and a water-soluble monomer in a set amount ratio and having an appropriate molecular weight can be obtained in the form of particles. The reason why a good coating resin can be produced by this method is not clear, but it is considered as follows. That is, when the above method is adopted, solution polymerization proceeds at the initial stage of polymerization to produce a low molecular weight copolymer having a monomer unit composition commensurate with the reactivity ratio, and when the polymerization further proceeds, the copolymer becomes Although used for precipitation, some of them are combined by a coexisting dispersion stabilizer to produce relatively stable dispersed particles. Since the dispersed particles, which are a copolymer of the oil-soluble monomer and the water-soluble monomer, are a copolymer of the oil-soluble monomer and the water-soluble monomer, the dispersed particles in the continuous phase are It is considered that since the oil-soluble monomer and the water-soluble monomer in the reaction are absorbed at the same time, a copolymer having a controlled molecular weight and a relatively uniform composition can be produced with good reproducibility and productivity.

There are many problems in other polymerization methods, for example, in emulsion polymerization, the molecular weight of the coating resin becomes too high, and the resin-coated carrier obtained from the fact that an emulsifier is mixed in the produced polymer is environmentally stable and electrostatically stable. It becomes inferior in sex. Further, in bulk polymerization or suspension polymerization, a copolymer containing a large amount of polar group-containing monomers may be formed before the polymerization or during the polymerization, resulting in unusable use. As described above, it has been impossible to produce a highly stable coating resin by the conventional general polymerization method.

The amount of anionic groups present in the copolymer produced by the method of the present invention is generally 0.001 to 2 mol / kg, preferably 0.01 to 1 mol / kg, based on the whole polymer. . Within this range, a good charge imparting action can be exhibited without humidity dependency. As the molecular weight of the polymer, the weight average molecular weight is generally 5000 to 1000000, particularly preferably 10000 to 10000 from the solubility in a solvent, the durability of the coating layer, and the adhesion with the core material.
It is good to use the one of 100000. Further, the glass transition point of the polymer is preferably 70 to 150 ° C., particularly 90 to 120 ° C., and a coating layer excellent in durability and heat resistance can be formed.

(Preferred Embodiment of the Invention) Monomer The oil-soluble monomer used in the present invention is a vinyl aromatic hydrocarbon or (meth) acrylic acid ester.

As a vinyl aromatic monomer, In the formula, R ₁ is a hydrogen atom, a lower alkyl group or a halogen atom, and R ₂ is a hydrogen atom, a lower alkyl group, a halogen atom, an alkoxy group, a nitro group, or a vinyl group. For example, styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, o
-, M-, p-chlorostyrene, p-ethylstyrene,
Divinylbenzene may be used alone or in combination of two or more kinds.

Further, as the (meth) acrylic acid ester monomer, a compound represented by the formula: In the formula, R ₃ is a hydrogen atom or a lower alkyl group, R ₄ is a hydrogen atom, a hydrocarbon group having up to 12 carbon atoms, a hydroxyalkyl group,
Or a vinyl ester group, an acrylic monomer such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, hexyl methacrylate,
2-ethylhexyl methacrylate, ethyl β-hydroxyacrylate, propyl γ-hydroxyacrylate,
Examples include σ-butyl acrylate, β-hydroxyethyl methacrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and the like.

On the other hand, as the water-soluble monomer, sulfonic acid, phosphoric acid,
It has a carboxylic acid type anionic group, and these acid groups may be in the form of a salt such as an alkali metal salt such as a sodium salt, an ammonium salt, an amine salt or a free acid, and suitable examples thereof are , Styrene sulfonic acid, sodium styrene sulfonate, 2-acrylamido 2-methylpropane sulfonic acid, 2-acid phosphooxypropyl methacrylate, 2-2-acid phosphooxyethyl methacrylate, 3-chloro 2-acid phosphooxyethyl methacrylate, acrylic Acids, methacrylic acid, fumaric acid, crotonic acid, tetrahydroterephthalic acid, itaconic acid, maleic acid and the like. Among these, it is preferable to use the sulfonic acid type from the viewpoint of excellent charge imparting action.

The composition ratio of the oil-soluble monomer and the water-soluble monomer is determined so that the solubility of the polymer in a solvent, the film-forming property after coating, the durability is good, and a sufficient charge imparting action is obtained. It is preferable to use it in a weight ratio of generally 70:30 to 99: 1, and particularly 80:20 to 98: 2.

Polymerization method As the water-miscible organic solvent used in the dispersion polymerization method which is a preferred production method in the present invention, lower alcohols such as methanol, ethanol and isopropanol; acetone, methyl ethyl ketone; ketones such as methyl butyl ketone; tetrahydrofuran, dioxane, etc. , Ethers such as ethyl acetate, and amides such as dimethylformamide are appropriately selected and used according to the kind of the monomer used.

The use ratio of water and a water-miscible organic solvent varies depending on the type of solvent and monomer, but is generally 40:60 to 5: 9.
From the weight ratio of 5, especially 30:70 to 10:90, the composition ratio may be selected so as to form a homogeneous solution phase. The ratio of the amount of the mixed solvent to the monomer used is 0.5 to 50 times by weight, preferably 5 to 25 times by weight, the mixed solvent.

As the dispersion stabilizer, a polymer-type dispersion stabilizer that is Tuesday in the mixed solvent described above, for example, polyacrylic acid, polyacrylic acid salt, polymethacrylic acid, polymethacrylic acid salt, (meth) acrylic acid- (meth) acrylic. Acid ester copolymers, acrylic acid-vinyl ether copolymers, methacrylic acid-styrene copolymers, carboxymethyl cellulose, polyethylene oxide, polyacrylamide, methyl cellulose, ethyl cellulose, hydroxylethyl cellulose, polyvinyl alcohol and the like are preferable, but nonionic. It is possible to use anionic or anionic surfactants. The dispersion stabilizer is preferably present in the system in an amount of 0.001 to 10% by weight, especially 0.1 to 3% by weight.

Examples of the polymerization initiator include azo compounds such as azobisisobutyronitrile, and peroxides such as cumene hydroperoxy t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, benzoyl peroxide and lauroyl peroxide. Those soluble in water-insoluble monomers are used. In addition, combinations of ionizing radiation such as γ-rays and accelerated electron beams and ultraviolet rays with various photosensitizers are also used.

The compounding amount of the azo compound and the polymerization initiator of the peroxide may be a so-called catalytic amount, and it is generally preferable to use the amount of 0.1 to 10% by weight based on the charged monomers. The polymerization temperature and time may be those known in the art, and in general, polymerization at a temperature of 40 to 100 ° C. for 1 to 50 hours is sufficient. The reaction system may be stirred gently so that a homogeneous reaction occurs as a whole, and in order to prevent the inhibition of polymerization by oxygen, the reaction system is replaced with an inert gas such as nitrogen to carry out the polymerization. May be. Copolymers produced by polymerization generally have a particle size of 0.1 to 10 μm, especially 0.5.
It can be obtained as a granular material having a size of 7 to 7 μm.

Examples of the core material coated with the resin produced by the production method of the present invention include iron oxide, reduced iron, copper, ferrite, nickel, cobalt and the like, alloys with these zinc and aluminum, and the like. Ferrite particles that are small in environmental and temporal changes and capable of forming soft ears are preferable. For example, Zn-based ferrite, Ni-based ferrite, Cu-based ferrite, Mn-based ferrite, Ni-Zn-based ferrite, Mn-
Examples thereof include Mg-based ferrite, Cu-Mg-based ferrite, Cu-Zn-based ferrite, and Mn-Cu-Zn-based ferrite. Especially, Cu-Z
N-type ferrite is preferable. The particle size of these magnetic materials is 10
To 200 μm, preferably 30 to 150 μm. Then, the copolymer is dissolved in a suitable solvent, if necessary, a curing agent, a resistance adjusting agent, etc. are added, and the coating is performed using a conventionally known coating method such as a dipping method, a fluidized bed method, or a spray drying method. The solvent component is removed and then dried to obtain a resin-coated carrier.

The coating amount of the core material is generally 0.1 to 20% by weight, and preferably 0.2 to 10% by weight.

The resin-coated carrier obtained by the above method effectively positively charges the toner because the anionic groups are uniformly and uniformly dispersed in the coating resin, and the resin itself is a single polymer. Therefore, it does not cause phase separation and has excellent durability, and stable image formation can be performed even when a developing operation is repeated for a long time.

 Hereinafter, the present invention will be described in detail with reference to examples.

(Example 1) According to the formulation shown in Table-1, styrene, sodium styrenesulfonate, polyacrylic acid, azobisisobutyronitrile and octyl thioglycolate were dissolved in a mixed solvent of alcohol and water, and 3 l of separa was added. Polymerization was completed by reacting for 12 hours at the temperature shown in Table 1 while stirring at 150 rpm in a bull flask at 150 rpm. The emulsion thus obtained was centrifuged to separate the particles, and three types of styrene-sodium styrenesulfonate copolymers having different molecular weights were obtained as white powders. The weight average molecular weight of N-1, N-2 and N-3 is 87,000 respectively.
It was 0, 21000 and 2400.

Ferrite particles having an average particle diameter of about 80 μm are used as the core material, and N-1 and N
-2 and N-3 toluene solutions (5 wt%) were sprayed to form a coating layer of 1 wt% on the core material, and then dried at 100 ° C for 2 hours to obtain a coating carrier C-1; C-2 and C-3 were obtained. N-
In the operation of preparing a toluene solution of 1, N-2 and N-3, N-1 was not easily dissolved in toluene and the viscosity of the solution was very high, but it is possible to form a coating layer on the core material. there were. N-2 and N-3 were easily dissolved in toluene, and the coating operation could be easily performed.

The C-1, C-2 and C-3 thus prepared and the positively chargeable toner prepared by the formulation of Table 2 are
The mixture was mixed at a ratio of 15 to obtain a developer. Each of these three types of developers was mounted on a laser printer LPX-1 (trade name, manufactured by Mita Kogyo Co., Ltd.), and 5,000 sheets at high temperature and high humidity (35 ° C, RH85%), followed by low temperature and low humidity (10 ° C, As a result of further performing a copying test on 5,000 sheets at RH 45%), no problems such as toner scattering, image fog and change in image density occurred in each environment. Further, this developer showed an appropriate charge amount under each environment, and the rising of charge was extremely high. Following a high-temperature high-humidity, low-temperature low-humidity copy test, and then a normal-temperature normal-humidity (20 ° C, RH60%) 10,000-copy test, a developer using C-1 and C-2 carriers was developed. Did not see any change in image quality,
The developer of C-3 carrier coated with a styrene-sodium styrenesulfonate copolymer having a weight average molecular weight of 2400 produced some image fog. When the C-3 carrier after the 20,000 copy test was observed with a scanning electron microscope, the coating resin on the carrier surface was partially peeled off. However, such a problem did not occur in a carrier obtained by coating a toluene solution of a styrene-sodium styrenesulfonate copolymer having an Mw of 2400 with a curing agent such as a melamine curing agent coated.

Example 2 According to the formulation shown in Table 3, styrene, phenylvinylphosphonic acid, acrylic acid-methyl methacrylate copolymer, azobisisobutyronitrile and octyl thioglycolate were mixed in an alcohol-water mixed solvent. After dissolution, the mixture was allowed to react for 12 hours at a temperature shown in Table 3 under stirring in a 3 l separable flask under a nitrogen stream at 150 rpm to complete the polymerization. The emulsion thus obtained was centrifuged to separate the particles, and white powdery resins P-1, P-2 and P-3 having different ratios of phenylvinylphosphonic acid were obtained.

Ferrite particles having an average particle diameter of about 80 μm are used as the core material, and P-1, P
-2 and P-3 toluene solutions (5 wt%) are sprayed to form a coating layer of 1 wt% on the core material, and then dried at 100 ° C for 2 hours to obtain a coating carrier C-4, C-5 and C-6 were obtained.

The C-4, C-5 and C-6 produced in this manner and the positively chargeable toner produced by the formulation of Table 2 are
The mixture was mixed at a ratio of 15 to obtain a developer. The amount of charge due to blow-off of each developer is shown in Table-2. Laser printer LPX-1 for these three types of developers
(Mita Kogyo Co., Ltd. product name)
5,000 sheets at ℃, RH85%, followed by low temperature and low humidity (10 ℃,
As a result of further copying test for 5,000 sheets at RH45%), C- using P-2 resin having a phosphate group ratio of 0.55 mol / kg.
The developers of No. 6 did not cause problems such as toner scattering, fog, and change in image density under each environment. However, P- with a phosphate group ratio of 0.01 mol / kg
With the C-5 developer using the No. 1 resin, toner scattering occurred only slightly. The C-6 developer using P-3 resin with a phosphoric acid group ratio of 1.1 mol / kg had no problems such as scattering and fog, but the image density was changed due to the changes in the environment of high temperature and high humidity and low temperature and low humidity. It has changed slightly.

Comparative Example 1 Ferrite particles having an average particle diameter of 80 μm were used as a core material, and an isobutylene ammonium maleate anhydride (Mw = 1.5 × 10 ⁶ ) aqueous solution (5 wt%) and polystyrene (Mw) were used by a fluidized bed coating method. = 1.5 × 10 ⁶ ) toluene solution (5 wt%) is sprayed from two nozzles to form a coating layer of 1 wt% on the core material, and then dried at 100 ° C. for 2 hours to obtain carrier C-7. Was produced.

The positively chargeable toner produced according to the formulation of Table-2,
The mixture was mixed at a ratio of 85:15 to prepare a developer. Using this developer, the same copying test as in Example 1 was conducted. As a result, good images were obtained on the first several hundreds of sheets, but fogging started to be noticeable on the image around the 1000th sheet, and toner scattering became remarkable after the 2000th sheet. It was confirmed that the coating resin was completely peeled off by observing the C-7 carrier, which had been subjected to the 2000 copy test, with a scanning electron microscope.

(Effects of the Invention) According to the present invention, the monomer composition ratio is uniform and the anionic groups are uniformly dispersed, resulting in a copolymer having a suitable molecular weight, which is excellent in adhesion to the core material and film formability. The carrier coating resin can be easily manufactured.

Continuation of the front page (56) Reference JP-A-62-178279 (JP, A) JP-A-62-187863 (JP, A) JP-A-63-313170 (JP, A) JP-A-63-313169 (JP , A) JP 58-86561 (JP, A) JP 63-198073 (JP, A) JP 1-167852 (JP, A)

Claims (1)

(57) [Claims] 1. At least one oil-soluble monomer selected from the group consisting of vinyl aromatic monomers and (meth) acrylic acid esters, and a sulfonic acid, phosphoric acid, or carboxylic acid type anionic monomer. At least one water-soluble monomer having a group, dispersion-polymerized in a mixed solvent of water and a water-miscible organic solvent and in the presence of a dispersibility stabilizer, the water-soluble monomer and an oil-soluble monomer A method for producing a coating resin for a carrier, which comprises recovering a copolymer with a body in the form of particles.