JPH04110860A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To enhance the electrostatic charge characteristic of a developer and the resolution of images and to obviate the generation of fogging in the background part of the images by compounding a specific binder resin and a specific metal complex into the magnetic toner. CONSTITUTION:The binder resin contg. at least a carboxyl group-contg. monomer as its constituting unit and having 2 to 20 acid value binder resin and the metal complex of (alkyl substd.) salicylic acid into the magnetic toner of this developer. A ferrite carrier or magnetite carrier is preferably used as the carrier. A styrene/acrylic acid 2-ethylhexyl/acrylic acid copolymer, etc., are usable as the above-mentioned resin and 3, 5-ditertiary butyl salicylic acid chromium complex, etc., are usable as the above-mentioned complex.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic developer containing a magnetic toner and a magnetic carrier.

(Prior Art and Problems to Be Solved by the Invention) Conventionally, methods for developing electrostatic latent images can be roughly divided into two-component developing methods that use a two-component developer mainly consisting of toner and carrier, and two-component developing methods that use a two-component developer mainly consisting of toner and carrier. There is a one-component developing method using a one-component developer, and various proposals have been made regarding these methods.

A two-component development method using a non-magnetic toner and a carrier as a two-component developer has the following advantages compared to a one-component development method:
There are some drawbacks as follows. ■A toner concentration sensor is required to control the mixing ratio of toner and carrier. ■The life of the developer is short. ■Developer stirring mechanism,
It requires careful handling and requires large equipment such as a developing machine.

On the other hand, the one-component development method has the following drawbacks.

■It is a charging member, sleeve, or plate, and compared to a carrier, it lacks charging stability and has weak charging ability. ■
The precision of the developing machine is required to uniformly form the magnetic plan. ■When using magnetic toner, it is inferior to non-magnetic toner in terms of transfer performance, fixing performance, environmental characteristics, and damage to the photoreceptor.

In order to overcome both of these problems, various proposals have been made regarding two-component development methods using magnetic toner and magnetic carrier as two-component developers, and some of them have been put into practical use. This developing method has the following advantages. ■A wide range of toner density is allowed, and a precise density sensor is not required. ■Since a carrier is used, triboelectric charging properties are good.

- It is easy to form a magnetic plan and does not require the precision of a developing machine as in the case of the one-component developing method. ■The content of magnetic material in the toner should be smaller than that of the [component system], and the fixing properties, transfer properties, and environmental characteristics should be at the same level as when using non-magnetic toner in a two-component developer. I can do it. ■Since there is no need to stir the developer, the structure of the developing machine is simple and can be designed compactly, similar to the one-component developing method.

As a two-component developer using such a magnetic toner, US Pat. No. 4,640,880 discloses one using a charged magnetic toner and a ferrite carrier. However, when the second developer is used at a higher specific toner density than a two-component developer using normal non-magnetic toner, sufficient charging characteristics cannot be obtained, and the image quality is not at a sufficiently satisfactory level. I couldn't say yes. In particular, there was a drawback that scattering, bleeding, etc. were inferior to those of a two-component developer using non-magnetic toner.

It melts due to the heat and pressure of the roll, and the fixed image spreads out, causing the characters to become flattened. This phenomenon is particularly
As in the two-component developer using the above-mentioned magnetic toner,
This problem occurs violently when the toner has a low chargeability and a large amount of toner development, and images with many fine lines cannot be resolved and characters may not be distinguishable. Further, as the softening point becomes lower, an offset phenomenon to the fixing roll is more likely to occur.

In order to solve this problem of characters being crushed and the offset phenomenon occurring, conventional methods have been proposed, such as increasing the molecular weight of the toner's binder resin, or adding a cross-linking agent during polymerization of the resin to form a gel. has been done.

With these methods, the problem of blurred characters and offset phenomenon may be improved, or the fixing strength may be weakened.

The present invention has been made in view of the above-mentioned circumstances in the prior art.

An object of the present invention is to provide a two-component electrophotographic developer containing a magnetic toner that has good fixing properties and anti-offset properties, and also exhibits good image characteristics without crushed characters.

Another object of the present invention is to provide an electrophotographic developer that has good charging characteristics, good resolution and sharpness of Ltl 21 images, and does not cause fogging in the background of the image. be.

[Means to solve the problem]

The present invention provides an electrophotographic developer containing a magnetic toner and a magnetic carrier, wherein the magnetic toner contains at least a carboxyl group-containing monomer as a constitutional unit, and the magnetic toner has an acid value of 2 to 2.
0 and a metal complex of salicylic acid or alkyl-substituted salicylic acid.

The present invention will be explained in detail below.

The binder resin used in the magnetic toner of the present invention contains at least a carboxyl group-containing monomer as a structural unit. Specific examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, maleic acid,
Examples include fumaric acid, malonic acid, succinic acid, and glutaric acid. When the carboxyl group-containing monomer is dicarboxylic acid, even if it is in the form of an acid anhydride, it may be styrene, methylstyrene, chlorostyrene, vinyltoluene, etc.), acrylic acid or methacrylic acid ester monomer (acrylic acid Methyl, ethyl acrylate, n-butyl acrylate, todenyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n- methacrylate
octyl, dodecyl methacrylate, stearyl methacrylate, etc.). These monomers alone
Alternatively, a mixture of multiple types can be used. The composition and molecular weight are appropriately determined depending on the softening point and glass transition point of the desired polymer.

In the binder resin of the present invention, the copolymerization ratio of the carboxyl group-containing monomer is set to 2 to
It may be determined to be between 2o. Normally, it is preferable that it is in the range of 5 to 2 degrees.

1. The acid value refers to the acid contained in 1 g of binder resin.
The amount of potassium hydroxide required for neutralization is shown in mg (in the formula, R1R2, R3 and R4 each represent a hydrogen atom or an alkyl group, and ~1 is Cr.

Indicates a metal atom such as Zn, Ni, Co, Cu, etc., and X' represents a counter ion (H'Na""NH4' etc.),
A metal complex of salicylic acid or alkyl-substituted salicylic acid is included.

As the metal complex of salicylic acid or alkyl-substituted salicylic acid, for example, those represented by the following general formula can be used.

In the following margin, it is assumed that when the components are melted and kneaded, they are easily thermally decomposed and the metal ions and carboxyl groups in the resin react to form an ionic crosslinked structure. As a result, the melt viscosity of the magnetic toner increases compared to the melt viscosity of the binder resin alone, and the increase in the binder resin significantly improves the off-center property, and also improves the image collapse phenomenon caused by heat pressure during fixing. It seems likely that

In the magnetic toner of the present invention, the degree of viscosity increase is as follows:
It depends on the content of carboxyl groups in the binder resin and the amount of salicylic acid or metal complex of alkyl-substituted salicylic acid added. The offset properties and the crushing phenomenon change depending on the degree of viscosity increase, and the higher the viscosity, the better the offset resistance and the crushing phenomenon of characters.

However, if the amount of carboxyl groups, which are crosslinking points, is too large, the viscosity due to crosslinking increases too much, resulting in a decrease in fixing strength and also causing a low-temperature offset phenomenon. Therefore, in the present invention, it is necessary to use a binder resin whose acid value is in the range of 2 to 2o.

On the other hand, if the amount of salicylic acid or a metal complex of alkyl-substituted salicylic acid is small, sufficient thickening due to crosslinking will not occur, resulting in high-temperature offset phenomena and crushed characters during fixing. Furthermore, if the amount added is too large, the toner may become charged too high because the metal complex of salicylic acid or alkyl-substituted salicylic acid itself has negative charging characteristics, which may result in an image of insufficient image quality. Can not. In addition, for reasons that are not clear, ultrafine powder is likely to be generated during pulverization and classification, resulting in a clouding phenomenon in the background of the image.

Furthermore, if the amount of the metal complex of salicylic acid or alkyl-substituted salicylic acid is small relative to the carboxyl groups of the binder resin, the environmental characteristics of the magnetic toner will deteriorate because the carboxyl groups that do not participate in crosslinking will remain.

As described above, the melt viscosity of a magnetic toner changes depending on the content of carboxyl groups in the binder resin and the amount of salicylic acid or a metal complex of alkyl-substituted salicylic acid. The amount of the complex to be added needs to be determined depending on the content of carboxy groups in the binder resin, and in the case of a binder resin with a high acid value, the amount to be added increases. Usually, salicylic acid or a metal complex of alkyl-substituted salicylic acid is added in an amount of 0.5 to 5 parts by weight based on the binder resin.

In the present invention, any known magnetic powder can be used as the magnetic powder contained in the magnetic toner. The amount of magnetic powder blended is usually set in the range of 20 to 70% by weight.

On the other hand, as the magnetic carrier in the present invention, any known carrier can be used; for example, spray-dried
A ferrite carrier or a granulated macnetite carrier produced by a granulation-firing process can be preferably used. Further, the surface of the magnetic carrier may be coated with a resin, and by applying the resin coat, the charging property can be stabilized and image characteristics and environmental stability can be improved.

In the electrophotographic developer of the present invention, the above-mentioned magnetic toner and magnetic carrier are usually mixed in a ratio of 1-0:90 to 90:1.
It is blended at a ratio of 0.

〔Example〕

The present invention will be explained below with reference to Examples and Comparative Examples.

Example 1 Magnetic tonastyrene-2-ethyl acrylate 61 weight 86 hexy-acrylic acid copolymer (acid value: 2, softening point: 134.2°C) (copolymerization ratio S
t・2EHA: AA=8019.7:0.3) Polypropylene (Viscol 66 Kano, manufactured by Sanyo Chemical Co., Ltd.) 2-% magnetic powder (
EPT-1100, manufactured by Toda Kogyo Co., Ltd.) 35% by weight Formula A below
The above components were mixed in a super mixer, melt-kneaded, pulverized and classified to obtain a magnetic 1-mer with an average particle size of 2 mrl.

Magnetic carrier Ferrai 1 - Core material (average particle size 5 (Dam, δS-
5-65e/g) treated with a coating agent consisting of a methyl methacrylate/ylanganate crosslinking agent.

Developer A developer was prepared by externally adding 05% by weight of colloidal silica to the above magnetic toner and mixing it with the above magnetic carrier at a mixing ratio of magnetic toner:magnetic carrier = 20:80.

Comparative Example 1 In place of the styrene-2-ethylhexyl acrylate copolymer in Example 1, styrene-2-ethylhexyl acrylate copolymer (acid value: O and softening point 130.4°C, copolymer) was used. Polymerization ratio 5t2EHA=80:2
A magnetic toner and a developer were prepared in the same manner as in Example 1, except that Example 1 was used.

Examples 2 to 4, Comparative Examples 2 and 3 In place of the styrene-2-ethylhexylacrylate-acrylic acid copolymer in Example 1, polymers having the acid value, softening point, and copolymerization ratio shown in Table 1 were used. A magnetic l-toner was prepared and a developer was prepared in the same manner as in Example 1, except that a magnetic lubricant was used.

Comparative Example 4 Instead of the metal complex represented by formula A in Example 2,
Comparative Example 5 A magnetic toner was produced under the same conditions as in Example 2, except that an azo chromium complex represented by the following formula B was used instead of the styrene-2-ethylhexyl acrylate-acrylic acid copolymer in Example 1. A magnetic toner and a developer were prepared in the same manner as in Example, except that styrene-2-ethylhexyl acrylate copolymer (acid value: 0 and softening point: 145.0"C) was used.

Next, an evaluation test was conducted using the developers of these Examples and Comparative Examples. A reversal development type laser printer equipped with a unipolar organic photoconductive photoreceptor was used as a testing machine.

Development was performed by rotating the photoreceptor and the sleeve in the same direction, and rotating the sleeve and the magnetic roll in opposite directions.

Table 1 summarizes the binder resin physical properties and toner compositions of the above Examples and Comparative Examples, as well as the evaluation results when the Examples and Comparative Examples were used.

In addition, the measurement of the 6 values in the table was performed as follows.

1) Acid value Indicates the number of mg of potassium hydroxide required to neutralize the acid contained in 1 g of resin.

2) Softening point measuring device Koka type flow tester (manufactured by Shimabara Seisakusho, CFT
-500 type) Measurement conditions 8 Die: 0.99mmφX1mm Load 20kgF Plunger, IC- Sample amount + 1.5g Heating rate 20℃/min Preheating temperature, 80℃ Preheating time = 300 sec Analysis method From the start point of outflow 1 of the plunger descent amount to the outflow stop point
The temperature at point /2 is read and taken as the softening point (unit: 0°C).

3) Rub the image fixed by the fixing strength tester with an eraser,
The residual rate of image density before and after was shown.

4) The temperature of the heat roll of the offset width tester was varied to measure the temperature range in which toner did not adhere to the heat roll when the roll passed.

5) Print after leaving the image characteristic tester and developer in each environment for 24 hours, and check the image density at Machhess density 1f (RD914).
It was measured with The environmental conditions are as follows.

N/N: 25℃/60%RH L/L: 10℃/20%RH H/H: 35℃/85%RH 6) Text is crushed The state of collapse after fixation of the thin line image was sensory evaluated.

○: There is no line width expansion, indicating a good condition.

△: Indicates a state in which some sagging occurs and the line width is widened.

×: The line width is completely thick and the linearity is also poor.

7) Overall judgment fixing strength = 85% or more, offset width 140-190°C
, Image characteristics: N/N-1, 30 or more, L/L-1
, 30 or more"2, H/H=1.30 or more, character swell:
Cases of ◯ and △ are indicated by ◯ as passing, and other cases are indicated as failing by ◯.

As is clear from Table 1 below, in Example 1, the softening point of the resin rose to 1398°C after toner production, and very good results were obtained for offset width and fixing properties. Ta. As for the text being crushed, it was at its limit.

In Example 2, the softening point of the resin increased to 1504°C. The offset width has been improved to 200°C on the high temperature side. There was very little blurring of characters, and images with good resolution and quality were obtained.

In Example 3, the offset resistance on the high temperature side was further improved than in Example 2.

In Example 4, the offset resistance on the high temperature side was further improved than in Example 3.

In Comparative Example C, the offset resistance on the high temperature side was poor;
An offset occurred on the image. Furthermore, after fixing, the characters and thin lines became very thick, resulting in an image of poor quality.

In Comparative Example 2, almost the same results as in Comparative Example 1 were obtained, with both offset and crushed characters being poor.

In Comparative Example 3, the softening point of the resin rose to 1B5.1°C after toner production, which was extremely high, and the fixing strength was 7.
The result was a poor 9%. Furthermore, due to the poor level of low-temperature offset, low-temperature offset may occur due to a decrease in the temperature of the heat roll due to continuous printing. Furthermore, under the L/L environment, a problem of low density occurred.

In Comparative Example 4, the toner had a low softening point and the level of high temperature offset was poor. In addition, a problem of low density occurred under the L/L environment. Furthermore, the characters were blurred, resulting in an image with poor resolution.

In Comparative Example 5, the softening point of the resin was as high as 1450,
Since the softening point after tonerization was also 143.9° C., the fixing strength was low.

〔Effect of the invention〕

As is clear from the above comparison, the electrophotographic developer of the present invention is as follows. In the magnetic toner, since a binder resin containing at least a carboxyl group-containing monomer as a structural unit and having an acid value of 2 to 20 is used, and a metal complex of salicylic acid or alkyl-substituted salicylic acid is contained in the binder resin, it is suitable for use in electrophotography according to the present invention. The developer has good fixing properties and anti-offset properties, and also exhibits good image characteristics without crushed characters. In addition, it has good charging characteristics, improves image resolution,
The contrast is good, and it is possible to form an image without haze in the image background.

Patent applicant: Tomoekawa Paper Mills Co., Ltd.

Claims (2)

[Claims] (1) In an electrophotographic developer containing a magnetic toner and a magnetic carrier, the magnetic toner contains at least a carboxyl group-containing monomer as a constituent unit, a binder resin having an acid value of 2 to 20, and a metal of salicylic acid or alkyl-substituted salicylic acid. An electrophotographic developer characterized by containing a complex. (2) The electrophotographic developer according to claim (1), wherein the magnetic carrier is a ferrite carrier or a magnetite carrier.