JPH07114221A - Electrophotographic carrier - Google Patents

Abstract

PURPOSE:To increase the tenacity of a coating film and to obtain excellent durability at normal temp. and normal humidity by coating the surface of a carrier with a silicone resin containing a silane coupling agent having specified physical properties. CONSTITUTION:The surface of the carrier is coated with a hardening silicone resin containing a crosslinking agent which generates >=9KCal/mol heat in hydrolysis with water. The obtd. silicone resin-coated carrier has higher mechanical durability and higher tenacity of the coating film due to the crosslinking reaction since the reactivity for coupling reaction is high. Further, in the coating process of the carrier, 10-500 pts.wt. of water to the silicone resin is mixed with the diluent solvent for the coating resin to be used for coating. In this process, the crosslinking point of the hardening silicone resin and hydrolysis of the silane coupling agent are promoted so that the reinforcing reaction is promoted. The surface energy of the silicone resin is increased even for a short time so that the adhesion property with the carrier core is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier in a developer used for developing an electric latent image or a magnetic latent image in electrophotography, electrostatic printing or the like. It relates to a significantly improved electrophotographic carrier.

[0002]

2. Description of the Related Art Carriers constituting a two-component developer are
Conductive carriers and insulating carriers are roughly divided, and oxidized or unoxidized iron powder is usually used as the conductive carrier, but in a developer containing the iron powder carrier as a component,
There are drawbacks that the triboelectric chargeability with respect to the toner is unstable and the visible image formed by the developer is fogged. That is, as the developer is used, the toner particles adhere to and accumulate on the surface of the iron powder carrier particles (spent toner), so that the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectrification property Becomes unstable, the image density of the visible image formed as a result decreases, and fog increases. Therefore, if a developer containing an iron powder carrier is continuously used for copying with an electronic copying apparatus, the developer deteriorates in a small number of times, so that it is necessary to replace the developer early, resulting in high cost. Will be things.

The insulating carrier is typically a carrier obtained by uniformly coating the surface of a carrier core material made of a ferromagnetic material such as iron, nickel or ferrite with an insulating resin. In the developer using this carrier, the toner particles are much less fused to the carrier surface than in the case of the conductive carrier, and at the same time, it is easy to control the triboelectrification property between the toner and the carrier, and the durability is improved. It has an advantage that it is particularly suitable for high-speed electronic copying machines because of its excellent service life.

There are various characteristics required for the insulating carrier, but as particularly important characteristics, appropriate chargeability, impact resistance, abrasion resistance, good adhesion between the core and the coating material, charge distribution Uniformity and the like can be mentioned.

In view of the above required characteristics, the conventionally used insulating carrier still has a problem to be improved, and a perfect one is not known so far.
For example, examples of using an acrylic resin or the like as a coating material for a carrier are disclosed in JP-A-47-13954 and JP-A-60.
It is disclosed in Japanese Patent Publication No.-208765. In addition, Japanese Patent Application Laid-Open No. Sho 6-1994 discloses that the molecular weight is particularly mentioned.
For example, it is known that the chargeability of the coated carrier is stabilized by controlling the molecular weight to be constant. However, in order to attach the coating resin to the carrier core material, it is easily affected by the conditions of the apparatus and the environment for coating, particularly humidity, and even if they are strictly controlled, the resin is stably attached to the core material, At present, there is nothing satisfying in order to have sufficient chargeability and durability.

On the other hand, it has been proposed to improve the durability by using a resin having a small surface energy as a coating layer in order to prevent the spent of the carrier such as toner fusion, and for example, a silicone resin is a resin having a small surface energy. Can be mentioned.

Silicone resins have the advantage of high water repellency in addition to low surface tension. On the other hand, since the silicone resin has poor adhesiveness, it has a drawback that it easily peels off when used in the coating layer.

In order to improve this drawback, for example, a method using a resin-modified silicone resin (JP-A-55-12756).
No. 9), a method of reacting another resin with vinylsilane (JP-A-56-32149), a method of using a mixture of trialkoxysilane and ethyl cellulose (USP3840464), an organosilicone terpolymer and a polyphenylene resin. A method using a mixture of the above (USP3849127) and the like have been proposed, but a high temperature of 300 ° C. or higher is required for forming the coating film, or the compatibility between the silicone resin and another resin is poor and the coating film is poor. However, there are problems such as non-uniformity and the expected characteristics cannot be obtained. It has also been proposed to form a coating film at a relatively low curing temperature (JP-A-55-127569).
However, since the adhesiveness is insufficient and the toughness of the coating film is insufficient, it is easily worn, and the carrier particles are agitated for a long period of time in the developing section such as a high-speed copying machine, so that the carrier particles become When the particles collide with each other or the surface of the photoconductor, or particles collide with each other, the silicone resin coating layer wears and peels off over time, and frictional charging changes from charging between the toner and the silicone resin to charging the toner and the carrier core material. Therefore, the charge amount of the developer cannot be kept constant and the image quality is deteriorated.

[0009]

SUMMARY OF THE INVENTION The main object of the present invention is to provide an electrophotographic carrier which has the above-mentioned conventional drawbacks, in particular, improved chargeability, mechanical strength, and adhesion to a core material and has good durability. To provide.

[0010]

[Means and Actions for Solving the Problems] As a result of various studies and investigations by the present inventors to improve the above-mentioned various drawbacks,
It has been found that the combined use of a specific compound in a silicone resin as a coating material is effective in improving the required properties of the coated carrier, and has completed the present invention.

Further, it has been found that the performance can be further improved by using a special method at the time of coating.

That is, according to the present invention, the carrier for electrophotography is characterized in that the surface thereof is coated with a curable silicone resin containing a crosslinking agent having a calorific value of 9 Kcal / mol or more during a hydrolysis reaction with water. Regarding

Further, according to the present invention, the above-mentioned silicone resin-coated carrier is carrier-coated by mixing 10 parts by weight to 500 parts by weight of water with respect to the silicone resin in a solvent for diluting the coating resin used for coating. The present invention relates to a carrier for electrophotography, which is characterized in that

It has also been proposed to use a modified silicone resin in order to improve the adhesiveness with the carrier core material, such as alkyd modification, epoxy modification, acrylic modification,
There are examples of using modified silicone resins such as polyester modification, phenol modification, melanin modification, urethane modification and the like, but this is not preferred because the surface energy increases and toner sticking easily occurs and the durability of the developer is impaired.

On the other hand, there has been proposed a method in which various additives are used in combination in order to improve the adhesiveness while keeping the low surface energy (Japanese Patent Laid-Open No. 2-33159).

These additives impart toughness in addition to adhesiveness due to reaction with the silicone resin or itself. However, the one disclosed in JP-A-2-33159 is an alkoxysilane, which has low reactivity as a coupling agent and its effect is insufficient, so that high toughness cannot be obtained.

When a large amount of alkoxysilane is added, the reactivity is low and the liquid tends to remain in a liquid state in the coating layer, further lowering the toughness of the coating film.

As a result of intensive studies by the present inventors, the mechanical durability of the obtained silicone resin-coated carrier is drastically improved by incorporating a highly reactive special compound as a silane coupling agent into the silicone resin. It became clear that it would increase.

The special silane coupling agent has a calorific value of 9 Kcal / mol or more during the hydrolysis reaction with water. The higher this value, the higher the reactivity of the coupling reaction and the crosslinking reaction. Means that the toughness of the coating is increased.

As a specific example of such a compound, the leaving group of the silane coupling agent is an oxime type (exothermic amount:
About 9 Kcal / mol or more), Acetone type (about 30)
Kcal / mol or more), acetic acid type (about 10 Kcal)
/ Mol or more), amide type (about 20 Kcal / mo)
1 or more) and the like, but are not limited thereto.

Alcohol-type silane coupling agents exist as leaving groups, but the calorific value is less than about 5 Kcal / mol and the reactivity is low, and sufficient durability can be obtained for the coating film on the carrier surface. Absent.

On the other hand, as a result of further studies by the present inventors for improving the durability of the coating film, the coated carrier obtained by adding water to the coating resin diluting solvent used in the production of the silicone resin coated carrier is obtained. It has been found that the durability and the charging characteristics of the are improved. This is because the crosslinking point of the curable silicone resin and the hydrolysis of the silane coupling agent are promoted, the curing reaction proceeds further, and the surface energy of the silicone resin increases for a short time, and It seems that the adhesion was improved.

In the present invention, the above-mentioned crosslinking agent having a calorific value of 9 Kcal / mol or more during the hydrolysis reaction with water is preferably 0.1 to 20 parts by weight, more preferably 0.3. By adding about 15 parts by weight, a carrier having excellent performance can be obtained.

Further, the amount of water added to the solvent for diluting the coating resin depends on the calorific value of the hydrolysis reaction of the cross-linking agent QKcal / mo.
1, when the amount of water relative to the silicone resin is M parts by weight, it is preferable that 200 ≦ Q × M ≦ 15000, more preferably 300 ≦ Q × M ≦ 13000, and the range of M is 10 ≦ M. ≦ 500 is appropriate.

If it is less than these ranges, the effect of promoting hydrolysis is small and the film strength of the coated carrier becomes insufficient. On the other hand, when it is larger than these ranges, the hydrolysis reaction is too fast and the curing reaction proceeds in the diluting solvent. For example, when the solution viscosity exceeds 200 cSt, the permeability to the carrier core material is lowered or the carrier core material is impaired. Granulation of particles is likely to occur.

Specific examples of the cross-linking agent having a calorific value of 9 Kcal / mol or more during the hydrolysis reaction used in the present invention include the followings, but the invention is not limited thereto.

[0027]

[Chemical 1]

The coating amount of the coating resin according to the present invention on the carrier core material is such that the resin solid content is 0.05% by weight to 10% by weight, preferably 0.1% by weight to 5% by weight. 0.0
If it is less than 5% by weight, the effect of coating the carrier core material with the resin is not sufficient, and the coating amount exceeding 10% by weight is meaningless, and there is a case where an excessive resin alone is present from the viewpoint of production. Absent.

The weight average particle diameter of the carrier core material used is 17 to 200 μm, preferably 20 to 65 μm. The measurement of the particle size distribution of the carrier is based on JIS-H2601. Further, the average particle size is from the obtained particle size distribution measurement value,
Calculate according to the following formula.

[0030]

[Equation 1]

The material of the magnetic particles used as the core material of the carrier of the present invention is 98% or more of Cu-Zn-Fe (metal composition ratio (5-20) :( 5-20) :( 30-8).
Ferrite particles having the composition of 0)) are preferable because the surface can be easily homogenized and the charging ability is stable, but are not particularly limited, and other flat, sponge-like, coin-like, spherical, true spherical, etc. Various forms of iron oxide powder, copper, manganese, cobalt,
Ferrite containing one or more of nickel, zinc, tin, magnesium, lead, strontium, barium, lithium and the like, particles made of a mixture of various resins and magnetic powder, and the like can be used.

For coating the core material with a resin, the curable resin and the crosslinking agent are dissolved in a suitable water-containing solvent, the core material is immersed in the resulting solution, and then the solvent is removed, dried and baked at high temperature. Or a method in which the core material is suspended in a fluidized bed, the copolymer solution is spray-coated, dried, and baked at a high temperature.

The carrier of the present invention thus obtained is mixed with a toner and used as a magnetic brush developer for developing an electrostatic latent image.

As the toner, any toner in which a colorant is dispersed in a binder resin and which is generally used in electrophotography can be used, and is not particularly limited.

When a two-component developer is prepared by mixing the carrier and the toner according to the present invention, the mixing ratio is 1.0 wt% to 12 wt%, preferably 2 wt% as the toner concentration in the developer. Good results are usually obtained with -9% by weight. If the toner concentration is less than 1.0% by weight, the image density is too low to be practical, and if it exceeds 12% by weight, fog and scattering in the machine are increased and the useful life of the developer is shortened.

[0036]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. "Parts" means "parts by weight".

Resin Coated Carrier Production Example 1 Curable Silicone Resin 100 parts Methyltrioxysilane 3 parts

MEK / H ₂ O = 95 /
Dilute with a mixed solvent of 5 to 5% by weight, and
After stirring at room temperature until the solution viscosity of 2 cSt exceeds 5 cSt, this solution is applied by a coating machine (Okada Seiko Co., Ltd .: Spiracoater)
The spherical ferrite particles having a Cu—Zn composition and having an average particle diameter of 45 μm were coated so that the resin coating amount was 0.5 parts by weight.

The resulting coated carrier was dried at 60 ° C. for 1 hour to remove the solvent, and then heated at 150 ° C. for 30 minutes to obtain a resin-coated carrier 1.

Resin Coated Carrier Production Examples 2 to 8 Resin Diluted Concentration of 5 in Resin Coated Carrier Production Example 1
% By weight, resin coating amount 0.5 part, drying at 60 ° C. for 1 hour, heating at 150 ° C. for 30 minutes, and the curable silicone resin are the same, but the crosslinking agent and the diluting solvent are changed and shown in Table 1. Such resin-coated carriers 2 to 8 were obtained.

[0041]

[Table 1]

The heat of reaction was determined as follows.

A flask containing 1 kg of water is covered with a heat insulating material, and a thermometer is set in advance. Here, 0.1 mol of crosslinking agent
And stir until the water temperature stops rising. The water temperature when the water temperature stops rising is T ₂ ℃, and the first water temperature is T ₁
The reaction heat can be calculated by the following approximate expression when the temperature is set to ° C.

(T ₂ −T ₁ ) × 10 (Kcal / mol)

Toner Production Example Polyester resin obtained by condensing 100 parts of propoxylated bisphenol and fumaric acid Phthalocyanine pigment 4 parts 4 parts of chromium complex of di-tert-butylsalicylic acid 4 parts were sufficiently premixed by a Henschel mixer and biaxial. The mixture was melt-kneaded by an extrusion-type kneader, cooled, coarsely pulverized to about 1 to 2 mm using a hammer mill, and then finely pulverized by an air jet type fine pulverizer. Further, the obtained finely pulverized product was classified to obtain a cyan powder having a negative triboelectrification property and a weight average particle diameter of 8.3 μm.

100 parts of the above colored powder and 1.0 part of titanium oxide fine powder (T805) were mixed with a Henschel mixer to obtain a cyan toner.

Example 1 The above-mentioned cyan toner and carrier 4 were mixed at a toner concentration of 5% to prepare a developer, and a color copying machine CLC-500 was prepared.
Table 2 shows the results of printing 10,000 images at 23 ° C./60% using an original document having an image area ratio of 25% (manufactured by Canon Inc.). Table 2 shows that the above-mentioned developers have little variation in the printing durability test, and the image quality after 10,000 sheets has no problem.
It turns out to be very good.

The following Comparative Examples and Examples are also shown in Table 2.

Example 2 An experiment similar to that of Example 1 was carried out using the carrier 1, and good results were obtained as shown in Table 2.

Example 3 The same experiment as in Example 1 was carried out using the carrier 2, but a slight toner scattering was observed after 10,000 sheets, but there was no problem and the other results were good. It was

Example 4 An experiment similar to that of Example 1 was carried out using the carrier 5, but after 10,000 sheets, the image quality slightly deteriorated, and the image density and fog increased slightly, but both were at a level with no problem. there were.

Example 5 Using the carrier 6, the same experiment as in Example 1 was carried out. However, the image quality slightly deteriorated after 10,000 sheets, and the image density and fog remained slightly higher from the initial stage through durability. All were at a level with no problem.

Comparative Example 1 Using the carrier 7, the same experiment as in Example 1 was carried out. After 10,000 sheets, the image quality slightly deteriorated, and the image density and fog, which were slightly higher in the initial stage, became higher. .

It is considered that since the content of water in the diluting solvent is small, the hydrolysis of the silicone resin and the crosslinking agent is slow and the durability after curing is insufficient.

Comparative Example 2 The same experiment as in Example 1 was conducted using the carrier 8, and the initial image quality was slightly low, and the image density and fog were high. After 10,000 sheets, the image quality was further deteriorated and the image density and fog were further increased.

Since the content of water in the diluting solvent is too high and the hydrolysis and cross-linking speeds are high, the viscosity of the diluting solution rises quickly, granulation of carrier particles easily occurs, and the charge amount decreases due to the decrease of the carrier surface area. It is considered that the carrier particles were deformed due to the damage of the granulated product during the durability test.

Comparative Example 3 Using the carrier 3, the same experiment as in Example 1 was carried out. After 10,000 sheets, the image quality slightly deteriorated, and the image density and fog also increased.

It is considered that the alkoxysilane has a low reaction heat of 5 Kcal / mol during hydrolysis and its reactivity is low, so that the curing reaction is insufficient and sufficient durability cannot be obtained.

[0059]

[Table 2]

The evaluation of fog was performed by REFL manufactured by Tokyo Denshoku Co., Ltd.
It was measured using ECTOMER MODEL TC-6DS, and for cyan toner images, it was calculated using the aver filter using the following formula. The smaller the number, the less fog.

Fog (reflectance) (%) = reflectance (%) of standard paper-reflectance (%) of non-image area of sample

[0062]

Industrial Applicability The carrier of the present invention is coated with a silicone resin containing a silane coupling agent having a specific physical property value (heat of reaction during hydrolysis) under specific coating conditions to thereby improve the toughness of the coating. And has excellent durability under normal temperature and humidity.

Claims (2)

[Claims] 1. The calorific value during the hydrolysis reaction with water is 9 Kc.
A carrier for electrophotography, the surface of which is coated with a curable silicone resin containing al / mol or more of a crosslinking agent. 2. The electrophotography according to claim 1, wherein 10 parts by weight to 500 parts by weight of water is mixed with the silicone resin in a solvent for diluting the coating resin used for coating to carry out carrier coating. For carrier.