JPH07333906A - Electrophotographic toner and production of toner - Google Patents

Abstract

PURPOSE:To obtain such an electrophotographic toner that can be fixed to offset resistance, and shows excellent fixing strength to a transfer sheet and image characteristics, by curing the toner particles containing a blocked isocyanate and a binder resin having hydroxyl groups in such a manner that the particle is cured stepwise toward the surface. CONSTITUTION:This toner particles contain at least a blocked isocyanate and a binder resin having hydroxyl groups, and the surface of the particle is cured in such a manner that the crosslinking density is stepwise increased from the inner part to the surface of the particle. Since the blocked isocyanate is added when the source material is mixed in the production process of the toner and melted and kneaded, the storage stability of the material is important. Thereby, it is preferable to use a isocyanate blocked with a blocking agent or an innernally blocked isocyanate. The amt. of the blocked isocyanate is determined according to the amt. of hydroxyl groups in the binder resin, and it is preferably to add the blocked isocyanate about 0.5-20wt.% of the binder resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner for a copying machine or printer which employs heat fixing.

[0002]

2. Description of the Related Art In recent years, electrophotographic copying machines and printers have been widely used in general households and the like, and have been reduced in energy consumption mainly for the purpose of multifunctionalization of copying machines or printers. (Reduction of power consumption), high speed for popularization in so-called gray area located at the boundary between printing machine and copying machine, or low roll pressure for simplification of fixing roll to reduce machine cost. Is desired. In addition, copiers equipped with a double-sided copy function and an automatic document feeder have become widespread with the sophistication of copiers, and therefore the fixing temperature of electrophotographic toner used in copiers and printers is low and There is a demand for a sheet having excellent offset properties and excellent fixing strength on a transfer sheet in order to prevent stains during double-sided copying and stains in the automatic document feeder.

[0003] In response to the above demands, in the prior art, proposals have been made of those in which the binder resin has improved molecular weight and molecular weight distribution. Specifically, attempts have been made to lower the fixing temperature by lowering the molecular weight of the binder resin. However, when the molecular weight is lowered, the melting point is lowered, but at the same time, the viscosity is also lowered, which causes a problem that an offset phenomenon occurs on the fixing roll. In order to prevent this offset phenomenon, a method of widening the low molecular weight region and the high molecular weight region of the molecular weight distribution of the binder resin, or cross-linking of the polymer portion has been performed. However, in this method, the glass transition temperature (Tg) of the resin has to be lowered in order to provide sufficient fixability, and it is unavoidable that the storage stability of the toner is impaired.

Conventionally, a method of adhering inorganic fine particles such as silica, titanium, alumina or the like, resin fine particles or the like to the toner surface has been used as a means for ensuring the preservability. However, it is difficult to completely uniformly coat the surface of the toner with these fine particles, and the toner having a low glass transition temperature (Tg) cannot sufficiently maintain the storage stability. Further, in order to completely cover the surface of the toner, a large amount of fine particles must be added, resulting in deterioration of fixing property and offset property. Furthermore, a large amount of fine particles adversely affect the charging characteristics and shorten the service life of the developer.

[0005]

The object of the present invention is to fix a toner at a low fixing temperature, to cause no practical problems even in the non-offset property, and to have excellent fixing strength on a transfer paper and excellent image characteristics. It is to provide a toner for electrophotography.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and its outline is a toner particle containing a binder resin containing at least a hydroxyl group and a blocked isocyanate. The toner for electrophotography is characterized in that the surface is cured so as to increase the crosslink density stepwise toward.

The present invention will be described in detail below. The blocked isocyanate used in the electrophotographic toner of the present invention is added by mixing the raw materials during the production of the toner and produced by melt-kneading, so that the storage stability of the material is important. Therefore, the isocyanate is preferably blocked with a blocking agent or internally blocked so that no problems occur even when it is stored under high temperature and high humidity such as summer and for a long period of time. Examples of these blocked isocyanates are the isophorone diisocyanate using ε-caprolactam as a blocking agent, manufactured by HULS Co., Ltd .: trade name: IPDI-B1065, IPDI-B1530, or internally blocked uretdione-bonded block isophorone diisocyanate. The Hills (HUL
S) product name: IPDI-BF1540. Also, 2,4 tolylene diisocyanate, 2,6 tolylene diisocyanate, diphenylmethane-4,4'-
Diisocyanate, hexamethylene diisocyanate and the like blocked with oxime can be mentioned. Examples of the oxime include formaldehyde oxime, acetoaldoxime, methyl ethyl ketoxime, and cyclohexanone oxime. Examples of the blocked isocyanate blocked with oxime include DM-60 and DM-160 manufactured by Meisei Chemical Industry Co., Ltd.

When the binder resin containing a hydroxyl group and the blocked isocyanate are crosslinked during the melt-kneading, the melt viscosity of the toner is increased and the fixing property is deteriorated. Therefore, it is necessary to set an appropriate temperature and time so that unreacted isocyanate remains during melt-kneading. The unreacted isocyanate can be achieved by kneading at a temperature not higher than the dissociation temperature of the blocked isocyanate. The unreacted isocyanate advances the reaction by heating the surface of the toner after melt-kneading and pulverizing and classifying or applying a mechanical impact force, and forms a cross-linked structure in the vicinity of the surface of the toner to form a glass transition temperature Tg of the binder resin. The storage stability is good even when the value is low. In addition, the inside of the toner is in an unreacted state,
Since the toner is heated during the fixing by the fixing roller, there is an advantage that the crosslinking further proceeds and the fixing strength of the image after fixing is improved. Although the content of the blocked isocyanate in the electrophotographic toner depends on the content of the hydroxyl group of the binder resin constituting the electrophotographic toner, it is approximately 0.5 to 20% by weight in the binder resin. Is preferred. If the content is less than 0.5% by weight, it is difficult to obtain a crosslinked structure because the effect as a crosslinking agent is small, and if the content is more than 20% by weight, the crosslink density with the binder resin is too high and the melt viscosity increases to fix Is not preferable because it deteriorates.

Next, materials other than the blocked isocyanate constituting the electrophotographic toner of the present invention, that is, a binder resin, a colorant and the like will be described. As the binder resin containing a hydroxyl group used in the present invention, a polyester resin is preferable because it can withstand a long life because of its high impact resistance and abrasion resistance and is excellent in fixability. . Examples of the diol component of the polyester resin include polyoxypropylene 2,2-2,2-bis (4-hydroxyphenyl) propane and polyoxypropylene (3,3) -2,2-bis (4-hydroxyphenyl). Propane, polyoxyethylene (2,0) 2,2
-Bis (4-hydroxyphenyl) propane, polyoxypropylene (2,0) -polyoxyethylene (2,
0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (6) -2,2-bis (4-)
Hydroxyphenyl) propane, ethylene glycol,
1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, and 1,6-hexanediol may be mentioned. Examples of trihydric or higher polyhydric alcohols include sorbitol,
1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, di Glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,3
5-trihydroxybenzene etc. are mentioned.

As the acid component, fumaric acid, maleic acid, phthalic acid, isophthalic acid, itaconic acid, glutaconic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sepacic acid, malonic acid, alkenylsuccinic acid, 1 , 2,4-benzenetricarboxylic acid, 2,
5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid, 1,2,4-butane tricarboxylic acid, 1,2,5-hexane tricarboxylic acid, 1,3-
Dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxy) methane, 1,
2,7,8-octane tetracarboxylic acid etc. are mentioned.

As the binder resin of the present invention, a styrene resin containing a hydroxyl group can also be used. The polymer is a suspension polymerization method of the monomers shown below, an emulsion polymerization method, a solution polymerization method,
It is synthesized by a bulk polymerization method or the like. As the monomer, styrene, α-methylstyrene, styrene such as chlorostyrene, methyl acrylate, ethyl acrylate,
Acrylic esters such as propyl acrylate, butyl acrylate, octyl acrylate, alkyl acrylate, methyl methacrylate, ethyl methacrylate,
Examples thereof include methacrylic acid esters such as propyl methacrylate, butyl methacrylate, octyl methacrylate, stearyl methacrylate, glycidyl methacrylate and alkyl methacrylate. Other copolymerization components include acrylonitrile, maleic acid, maleic acid ester, methyl methacrylate, methyl acrylate, vinyl chloride, vinyl acetate, vinyl benzoate, vinyl methyl ketone, vinyl hexyl ketone, vinyl methyl ether, vinyl ethyl ether, A vinyl monomer such as vinyl isobutyl ether may be contained in an amount of 30% by weight or less based on the polymer. Parahydroxystyrene, hydroxyethylhexyl acrylate, hydroxyethyl methacrylate and the like are contained as the hydroxyl group-containing monomer.

The hydroxyl value of the binder resin is preferably 1 or more and 100 or less. If the hydroxyl value is less than 1, sufficient cross-linking cannot be performed because the number of reaction points with isocyanate is small, resulting in 100
When it is larger than the above range, the moisture resistance is deteriorated when the unreacted functional group remains, and the charging property of the toner in a humid environment is deteriorated, which is not preferable. The hydroxyl value referred to here is a value measured by the method specified in JIS K 0070. The binder resin has a glass transition temperature (Tg) of 60.
It is preferably below ℃. If the Tg is 60 ° C. or higher, sufficient fixing strength cannot be obtained. Further, there is no problem in storage stability even if the surface crosslinking by the isocyanate of the present invention is not performed. The Tg is measured by a differential scanning calorimeter (hereinafter DSC).
It is measured with). Examples of the measuring device include a differential scanning calorimeter SSC-5200 manufactured by Seiko Instruments Inc. As measurement conditions, about 10 mg of resin is weighed, placed in an aluminum cell, placed on a DSC, and 50 ml of N ₂ gas is blown therein for one minute. Then, the temperature is raised from 20 ° C to 150 ° C at a rate of 10 ° C per minute,
Next, the process of quenching from 150 ° C. to 20 ° C. is repeated twice, and the amount of absorbed heat at that time is measured. Here, Tg indicates the temperature at the intersection of the baseline at the second measurement and the tangent line showing the maximum slope from the endothermic start to the end point.

As the coloring agent, carbon black, nigrosine dye, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate and mixtures thereof, Others can be mentioned. It is necessary that these colorants are contained in a sufficient ratio to form a visible image with a sufficient density. Usually, the colorant is about 1 to 20 parts by weight with respect to 100 parts by weight of the binder resin. The ratio of

In the method for producing the toner of the present invention, first, a binder resin containing at least a hydroxyl group, a blocked isocyanate, a colorant and other additive components are mixed to obtain a mixture, and the mixture is kneaded at a temperature not higher than the dissociation temperature of the blocked isocyanate. . As a melt kneader, a roll mill, a pressure kneader,
You can use a Banbury mixer or an extruder. After the kneading, the particles are pulverized by using a pulverizer such as a jet mill or a turbo mill, and then the toner particles are obtained by using an air classifier to have a desired particle size distribution. Thereafter, the toner particles are subjected to heat treatment or mechanical impact to gradually increase the crosslink density toward the surface of the toner particles, whereby the electrophotographic toner of the present invention is manufactured. A certain degree of heat treatment means is required to crosslink the surface of the binder resin with the blocked isocyanate, and as the heat treatment means, mixers that give high-speed shearing force, such as super mixer, Henschel mixer, turbulizer, etc. are used. It is possible. By being stirred by these mixers, frictional heat is generated on the toner surface and the crosslinking reaction proceeds. When it is desired to further accelerate the crosslinking, means such as heating hot water through the jacket of the mixer or blowing hot air may be used together.

In the present invention, the technical means for stepwise increasing the crosslink density toward the surface of the toner particles is to control the set temperature and time of a mixer as a heat treatment means or a surface reformer. Yes, for example, in the case of a hybridizer such as Nara mechanic, 600
It can be carried out by treatment at 0 RPM for 10 hours. Also, in order for the surface of the toner particles to begin to harden,
The dissociation temperature of the blocked isocyanate is 140 to 15
A heating condition of 0 ° C. is required. One of the conditions for the start of curing is that 20 g of toner particles are put in a 200 cc polyethylene bottle and left in a thermostatic chamber kept at 50 ° C. for 16 hours without blocking between particles. . On the other hand, when heat curing progresses and the crosslink density disappears in a stepwise manner from the surface to the inside, and all particles are cured, a guideline for the melting start temperature by a Koka type flow tester is 100
This is the case when the temperature rises above ℃.

Further, in addition to the above method, the toner particles may be applied to a surface modifier such as a hybridizer (manufactured by Nara Machinery Co., Ltd.) or Ongmill (manufactured by Hosokawa Micron Co., Ltd.) sold as a surface modifier. is there. Further, the heat treatment may be carried out by using a heat fluidized bed such as a surfing system (manufactured by Hosokawa Micron Corp.) for the toner particles. In order to further accelerate the cross-linking of the surface, a heat treatment may be performed after the catalyst for promoting the cross-linking of the blocked isocyanate is attached to the surface of the toner particles. The catalyst in this case is triethylamine, triethylenediamine, tin octoate, dibutyltin di (2-ethylhexoate), dibutyltin dilaurate, 2-ethylhexoate lead, o-phenylsoda, potassium oleate, bismuth nitrate, titanic acid. 2-Ethylhexyl, tin chloride, iron chloride, iron 2-ethylhexoate, cobalt 2-ethylhexoate, zinc naphthenate, antimony trichloride and the like can be used.

Regarding the melting characteristics of the toner, the melting start temperature of the toner is 6 in order to improve the fixing property at a lower temperature.
It is preferably 0 ° C or higher and 100 ° C or lower. If it is higher than 100 ° C., the fixing property is not sufficient, and if it is lower than 50 ° C., the blocking property is deteriorated and the storage stability may be deteriorated. The melting start temperature means the temperature at which the plunger starts to fall. Measuring instrument: Shimadzu's advanced flow tester CF-500 Measuring condition: Plunger: 1 cm ² Die diameter: 1 mm Die length: 1 mm Load: 20 KgF Preheating temperature: 50-80 ° C Preheating time: 300 sec Temperature rising rate : 6 ° C / min

The electrophotographic toner of the present invention is a particle obtained by appropriately dispersing and containing other toner components such as a charge control agent, a release agent and a magnetic material in the above-mentioned blocked isocyanate, binder resin and colorant. And the average particle size is in the range of 5 to 20 μm. A toner for electrophotography may be formed by adding and mixing a fluidity improver made of fine silica powder or the like to the particles thus obtained.

The electrophotographic toner of the present invention is mixed with a carrier composed of iron powder, ferrite, granulated magnetite or the like, and is used as a one-component developer without being mixed with a two-component developer or a carrier. Good.

[0020]

EXAMPLES The present invention will be described below based on examples. In the examples, "part" means "part by weight". Synthesis of Binder Resin Containing Hydroxyl Group Condensation polymerization using 85 mol% bisphenol A ethylene oxide adduct as an alcohol component, 15 mol% trimethylolpropane, 10 mol% trimellitic acid as an acid component, and 85 mol% dodecenylsuccinic acid. Then, a polyester resin (A) having a number average molecular weight of 7,500, a weight average molecular weight of 52,000, a hydroxyl value of 30, a Tg of 47 ° C. and a melting start temperature of 88.5 ° C. was obtained.

Example 1 The raw materials having the above blending ratios are mixed with a super mixer, hot melt kneaded with a twin-screw kneader, pulverized with a jet mill, and then classified with a dry air stream classifier to obtain an average particle diameter of 10
μm toner particles were obtained. The melting start temperature of the toner particles was 88.1 ° C. Then, the toner particles 10
0 parts by weight and 0.1 parts by weight of dibutyltin dilaurate were put into a Henschel mixer and stirred for 5 minutes.
Then, the obtained toner particles with a catalyst were treated with a hybridizer (manufactured by Nara Machinery Co., Ltd.) at 6000 RPM for 10 minutes. Further, 100 parts of the toner particles and 0.4 parts of hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corporation) are stirred for 1 minute in a Henschel mixer, and the hydrophobic silica is adhered to the surface of the particles to obtain the particles of the present invention. An electrophotographic toner was obtained.

Example 2 The raw materials having the above blending ratios are mixed with a super mixer, hot melt kneaded with a twin-screw kneader, pulverized with a jet mill, and then classified with a dry air stream classifier to obtain an average particle diameter of 10
μm toner particles were obtained. The melting start temperature of the toner particles was 88.8 ° C. Then, the toner particles 10
0 parts by weight and 0.1 parts by weight of dibutyltin dilaurate were put into a Henschel mixer and stirred for 5 minutes.
Then, the obtained toner particles with a catalyst were treated with a hybridizer (manufactured by Nara Machinery Co., Ltd.) at 6000 RPM for 10 minutes. Further, 100 parts of the toner particles and hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corporation) 0.4
The resulting mixture was stirred for 1 minute in a Henschel mixer, and hydrophobic silica was adhered to the surface of the particles to obtain the electrophotographic toner of the present invention.

Example 3 The structural formula of DM-60 is as follows.

[0024]

[Chemical 1]

Toner particles having an average particle diameter of 10 μm are prepared by mixing the raw materials having the above mixing ratios with a super mixer, hot-melt kneading them with a twin-screw kneader, pulverizing them with a jet mill, and then classifying them with a dry air stream classifier. Got The melting start temperature of the toner particles was 88.0 ° C. Then, 100 parts by weight of the toner particles and 0.1 part by weight of dibutyltin dilaurate were put into a Henschel mixer and stirred for 5 minutes. Then, the obtained toner particles with a catalyst were treated with a hybridizer (manufactured by Nara Machinery Co., Ltd.) at 6000 RPM for 10 minutes. Further, 100 parts of the toner particles and hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corporation).
0.4 part was stirred in a Henschel mixer for 1 minute, and hydrophobic silica was attached to the surface of the particles to obtain an electrophotographic toner of the present invention.

Example 4 The structural formula of DM-160 is as follows.

[0027]

[Chemical 2]

Toner particles having an average particle diameter of 10 μm are prepared by mixing the raw materials having the above mixing ratios with a super mixer, hot-melt kneading with a twin-screw kneader, crushing with a jet mill, and then classifying with a dry airflow classifier. Got The melting start temperature of the toner particles was 88.5 ° C. Then, 100 parts by weight of the toner particles and 0.1 part by weight of dibutyltin dilaurate were put into a Henschel mixer and stirred for 5 minutes. Then, the obtained toner particles with a catalyst were treated with a hybridizer (manufactured by Nara Machinery Co., Ltd.) at 6000 RPM for 10 minutes. Further, 100 parts of the toner particles and hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corporation).
0.4 part was stirred in a Henschel mixer for 1 minute, and hydrophobic silica was attached to the surface of the particles to obtain an electrophotographic toner of the present invention.

Example 5 The raw materials having the above blending ratios are mixed with a super mixer, hot melt kneaded with a twin-screw kneader, pulverized with a jet mill, and then classified with a dry air stream classifier to obtain an average particle diameter of 10
μm toner particles were obtained. The melting start temperature of the toner particles was 89.2 ° C. Then, 100 parts by weight of the toner and 0.1 parts by weight of dibutyltin dilaurate were put into a Henschel mixer and stirred for 5 minutes. Then, the obtained toner particles with a catalyst were treated with a hybridizer (manufactured by Nara Machinery Co., Ltd.) at 6000 RPM for 10 minutes. Further, 100 parts of the toner particles and 0.4 part of hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corporation) are stirred in a Henschel mixer for 1 minute to attach the hydrophobic silica to the surface of the particles, and thus the present invention To obtain a toner for electrophotography.

Comparative Example 1 A comparative electrophotographic toner was obtained in the same manner as in Example 1 except that blocked isophorone diisocyanate was not used.

Comparative Example 2 A toner was produced in the same manner as in Example 1 except that the following resin (B) having no hydroxyl value was used in place of the polyester resin (A). Styrene having a weight average molecular weight of 10 × 10 ⁵ and a number average molecular weight of 4 × 10 ⁵ (75 parts by weight)-
20 parts by weight of butyl acrylate (25 parts by weight) copolymer (3), weight average molecular weight 9 × 10 ³ and number average molecular weight 3 × 1
0 ³ styrene (75 parts by weight) -butyl acrylate (2
5 parts by weight) 80 parts of the copolymer (4) were mixed, and the molecular weight was 8 × 10 ⁵ and 5.5 × 10 ⁵ in the GPC chromatogram.
Hydroxyl value having peak position at ^{3 0} mgKOH / g, T
A styrene-acrylic copolymer (B) having a melting point of 52 ° C. and a melting start temperature of 97.0 ° C. was obtained.

Comparative Example 3 The raw materials having the compounding ratio of Example 1 were mixed in a super mixer, melt-kneaded by a twin-screw kneader, pulverized by a jet mill, and then classified by a dry air stream classifier to obtain an average particle diameter. Is 10
Particles of μm were obtained. The melting start temperature of this toner is 88.
It was 1 ° C. Then, the particles 10 were subjected to no heat treatment.
Electron for comparison was prepared by stirring 0 part and 0.4 part of hydrophobic silica (trade name: Cabosil TS-530 manufactured by Cabot Corp.) in a Henschel mixer at room temperature for 30 seconds to attach the hydrophobic silica to the surface of the particles. A photographic toner was obtained.

Comparative Example 4 The catalyst-attached toner particles obtained in Example 1 were used in a swirling fluidized bed dryer (trade name FBS-3) manufactured by Okawara Seisakusho Co., Ltd. for 150 times.
It was treated at 20 ° C. for 20 minutes to obtain a comparative electrophotographic toner. The melting start temperature of this toner was 130.1 ° C.

To compare the performance of electrophotographic toners,
The following items were tested. (1) Fixing Strength First, 4 parts of each of the electrophotographic toners obtained in the above Examples and Comparative Examples were mixed with 96 parts of a ferrite carrier (trade name: FL-1020 manufactured by Powdertech Co., Ltd.) not coated with a resin. To produce a two-component developer. Next, a commercially available copying machine (trade name: SF-9, manufactured by Sharp Corporation) is used using the developer.
800), a plurality of belt-shaped unfixed images having a length of 2 cm and a width of 5 cm were formed on an A4 transfer paper. Next, a heat fixing roll having a surface layer made of fluororesin (Teflon, a product name of DuPont) and a pressure fixing roll having a surface layer made of silicone rubber are paired to rotate a fixing device with a roll pressure of 1K.
The surface temperature of the heat fixing roll is adjusted to 120 ° C. by adjusting g / cm ² and roll speed to be 50 mm / sec.
And the toner image was fixed on the transfer paper on which the unfixed image was formed. Then, the formed fixed image was rubbed with a cotton pad, and the fixing strength was calculated by the following formula to be used as an index of low energy fixing property. As the image density, a reflection densitometer RD-914 manufactured by Macbeth was used. Fixing strength (%) = image density of fixed image after rubbing / image density of fixed image before rubbing × 100

(2) Storage Stability First, the storage stability of each of the electrophotographic toners obtained in Examples 1 to 5 and Comparative Examples 1 to 4 was evaluated. Evaluation is Toner 20
g in a polyethylene bottle of 200 CC, 50 ℃
It was left for 16 hours in a constant temperature bath kept in the atmosphere of and cooled to room temperature. The toner after standing was taken out, and the blocking state of the toner was visually observed. Evaluation is based on the following criteria.
◎ A state where there is no fusion between the toners and there is no difference from the state before leaving. ○ The fluidity is slightly deteriorated, but no coarse aggregates are found. △ Agglomeration of toner can be seen, but it can be unraveled immediately by pressing lightly with your finger. B. A state in which coarse particles that do not collapse even if pressed with a finger due to fusion of toner particles are generated. Table 1 shows the test results of the above items.

[0036]

[Table 1]

As is clear from the test results in Table 1, the electrophotographic toner of the present invention has a fixing strength of 80% or more at a fixing temperature of 120 ° C., and is confirmed to have a fixing strength practically sufficient. On the other hand, in Comparative Examples 1 to 3, it was confirmed that blocking occurred in the storage stability test and there was a problem in practical use. In Comparative Example 4, blocking did not occur, but the fixing strength was low and there was a problem. Also,
As a result of conducting a continuous copy test up to 10,000 sheets with a commercially available copying machine (Toshiba Co., Ltd., trade name: BD-3801) using each developer in the above item (1), in all of Examples 1 to 4. , The triboelectric charge amount is 10,000 from the beginning
The value changes from -20 μc / g to -25 μc / g between sheets, and the image density changes from 1.45 to 1.40 between the initial and 10000 sheets. It was confirmed that there was not. The copied original is A4 with a black portion of 6%, and the triboelectric charge amount is measured by using a blow-off triboelectric charge amount measuring device manufactured by Toshiba Chemical Co.
As the image density, a reflection densitometer RD-914 manufactured by Macbeth was used.

[0038]

The electrophotographic toner of the present invention has the effects that it can be fixed at a low temperature, is excellent in storability, and is capable of obtaining a sufficient number of image densities.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 22, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

In the method for producing a toner of the present invention, first, a binder resin containing at least a hydroxyl group, a blocked isocyanate, a colorant and other additive components are mixed to obtain a mixture, which is kneaded at a temperature not higher than the dissociation temperature of the blocked isocyanate. To do. As a melt kneader, a roll mill, a pressure kneader,
You can use a Banbury mixer or an extruder. After the kneading, the particles are pulverized by using a pulverizer such as a jet mill or a turbo mill, and then the toner particles are obtained by using an air classifier to have a desired particle size distribution. Thereafter, the toner particles are subjected to heat treatment or mechanical impact to gradually increase the crosslink density toward the surface of the toner particles, whereby the electrophotographic toner of the present invention is manufactured. A certain degree of heat treatment means is required to crosslink the surface of the binder resin with the blocked isocyanate, and as the heat treatment means, mixers that give high-speed shearing force, such as super mixer, Henschel mixer, turbulizer, etc. are used. It is possible. By being stirred by these mixers, frictional heat is generated on the toner surface and the crosslinking reaction proceeds. When it is desired to further accelerate the crosslinking, means such as heating hot water through the jacket of the mixer or blowing hot air may be used together.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

In the present invention, the technical means for stepwise increasing the crosslink density toward the surface of the toner particles is to control the set temperature and time of a mixer as a heat treatment means or a surface reformer. can, for example, in the case of a hybridizer manufactured by Nara machinery Co., Ltd., 600
It can be carried out by treatment at 0 RPM for 10 hours. Also, in order for the surface of the toner particles to begin to harden,
The dissociation temperature of the blocked isocyanate is 140 to 15
A heating condition of 0 ° C. is required. One of the conditions for the start of curing is that 20 g of toner particles are put in a 200 cc polyethylene bottle and left in a thermostatic chamber kept at 50 ° C. for 16 hours without blocking between particles. . On the other hand, when heat curing progresses and the crosslink density disappears in a stepwise manner from the surface to the inside, and all particles are cured, a guideline for the melting start temperature by a Koka type flow tester is 100
This is the case when the temperature rises above ℃.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031] A toner was prepared except for using the resin (B) described below is not in Comparative Example 2 Polyester resin (A) of the cash forte hydroxyl value in the same manner as in Example 1. Styrene having a weight average molecular weight of 10 × 10 ⁵ and a number average molecular weight of 4 × 10 ⁵ (75 parts by weight)-
20 parts by weight of butyl acrylate (25 parts by weight) copolymer (3), weight average molecular weight 9 × 10 ³ and number average molecular weight 3 × 1
0 ³ styrene (75 parts by weight) - butyl acrylate (2
5 parts by weight) 80 parts of copolymer (4) were mixed, and the molecular weight was 8 × 10 ⁵ and 5.5 × 10 ⁵ in the GPC chromatogram.
Hydroxyl value having a peak position at ^{3 0} mgKOH / g, T
A styrene-acrylic copolymer (B) having a melting point of 52 ° C. and a melting start temperature of 97.0 ° C. was obtained.

Claims (7)

[Claims] 1. An electrophotographic toner particle containing a binder resin containing at least a hydroxyl group and a blocked isocyanate, which is cured so as to gradually increase the crosslinking density toward the surface of the particle. For toner. 2. The toner for electrophotography according to claim 1, wherein the binder resin containing at least a hydroxyl group has a glass transition temperature of 60 ° C. or lower. 3. The melting start temperature of the toner is 60 ° C. or higher and 10
The toner for electrophotography according to claim 1, which has a temperature of 0 ° C. or lower. 4. The electrophotographic toner according to claim 1, wherein the binder resin has a hydroxyl value of 1 or more and 100 or less. 5. The toner for electrophotography according to claim 1, wherein the binder resin containing a hydroxyl group is a polyester resin. 6. A toner resin is prepared by melt-kneading and pulverizing a mixture containing a binder resin containing at least a hydroxyl group and a blocked isocyanate as a main component, and then heat-treating the toner particles or a machine. A method for producing a toner for electrophotography, characterized in that the crosslink density is gradually increased toward the surface of the toner particles by applying a dynamic impact force. 7. The method of producing a toner for electrophotography according to claim 6, wherein after the curing catalyst is attached to the surface of the toner particles, heat treatment or mechanical impact is applied.