JPS5840738B2 - Magnetic toner for developing electrostatic images - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves fixing properties when applied to magnetic toner for developing electrostatic images (hereinafter referred to as magnetic toner) used in electrophotography, electrostatic recording, and electrostatic printing and fixed by pressure. The objective is to provide a magnetic toner that has good properties and, in addition, excellent fluidity and image quality.

Magnetic toners that are fixed by pressure include: (1) When a powder image passes through a pressure roll, a pressure above a certain level is required to crush the toner on the powder image, but one with a low pressure; .

(2) The powder image passes through a pressure roll and is fixed on the recording paper, but the fixed image is easily peeled off due to external force.
Something that doesn't leave.

(3) The magnetic toner has good fluidity, is supplied to the magnetic roll extremely smoothly, forms a homogeneous image, and has high resolution.

is a desirable magnetic toner.

In conventional and commonly used magnetic toners that are fixed by pressure, the pressure required for fixing is a linear pressure of 25 to 40
kg/cfrL is required.

In order to obtain a linear pressure of 35 kg/crn, an A4 width (
297 mm), the weight of the pressure fixing machine body is approximately 20 kg.
This is a cause of increasing the weight of copying machines and the like.

As described above, the necessity of a large linear pressure is one of the reasons for preventing the spread of the pressure fixing method.

Further, the biggest drawback of pressure fixing is that it has poor fixing properties and the fixed image easily peels off and comes off.

That is, in view of the above-mentioned background, the present invention provides a magnetic toner that is fixed by pressure and does not have the above-mentioned conventional drawbacks by controlling the particle size distribution of magnetic toner powder.

The inventors discovered a mechanism in which magnetic toner is crushed in a pressure roll,
By elucidating the mechanism of fixation to recording paper and the mechanism by which a fixed image peels off and separates due to external force, we have developed a system that has good fixing properties at low pressure, uniform fixing properties in each part of the image, and fluidity. In addition, we have created a magnetic toner with excellent image quality.

There are three methods for fixing magnetic toner on recording paper: a heat fixing method, a pressure fixing method, and a method using both heat and pressure.

The magnetic toner obtained by the present invention exhibits its effects best when fixed by pressure, but it can also be used in other ways.

The present invention will be explained below using examples.

Example 1 High-density polyethylene wax (Mitsui Petrochemical product name r2
00Pj) 60 parts by weight, ethylene vinyl acetate copolymer (
10 parts by weight of Mitsui Polychemicals product name "#310" and iron oxide (Toda Industries product name 1'-EPT-500j)
A toner raw material consisting of 70 parts by weight was heated and kneaded using a roll, and then made into particles having two or less piles using a rotoplex pulverizer.

Of the obtained pulverized product, 45 parts by weight was pulverized using a pin mill (Alpine trade name "160ZJ") at 1200 Orpm, and the remaining 55 parts by weight was pulverized at 1800 Orpm.

To the powder obtained here, 1.5 parts by weight of carbon black (Mitsubishi Kasei product name "#44") was added, and the mixture was placed in a super mixer (Wakoku Seisakusho product name rsMG-20J) in a 45'C-53 atmosphere. was used for 3 minutes at 1900 rpm.

The powder thus obtained was classified using a wind classifier (Alpine trade name "FDO32Sj").

This magnetic toner particle size analyzer (Coulter Electronics Co., Ltd. product name "Coulter Counter Model TA-nj'")
), as shown in FIG. 1, a magnetic toner with a particle size distribution having two peaks at a particle size of 50 μm or less was obtained.

Example 2 A magnetic toner was obtained using the same composition and the same apparatus as in Example 1.

However, the difference from Example 1 as a condition is that the rotation speed of the pin mill was set to 1400 Orpm and 1800 Orpm.

The particle size distribution of the magnetic toner thus obtained was measured using a particle size analyzer (trade name: Coulter Counter Model TA-IIJ, manufactured by Coulter Electronics Co., Ltd.), and the result showed a particle size distribution as shown in Figure 2. .

The magnetic toners obtained in Example 1 and Example 2 had good fluidity, the magnetic toner was smoothly supplied to the magnetic roll, the image was homogeneous, the resolution was high, and the weight was 17 kg/cI.
When fixing was performed using a pressure fixing machine with a linear pressure of rL, sufficient fixing properties were shown.

In addition, the weight of the pressure fixing device to generate a linear pressure of 17 kg/cm is only 7.6 kgL, and therefore the structure is simple and lightweight, so it is expected that it will become popular in the future.

As shown in Figures 1 and 2, the fixed image of magnetic toner, which is an aggregate of particles of 50 μm or less and has two peaks in particle size distribution, is determined by a peel test with cellophane tape, a peel test with an eraser, and a peel test with an eraser. It has excellent results in various fixability evaluation tests such as bending tests and finger rubbing tests.

In particular, in a finger rubbing test, the magnetic toner of the above example is much less likely to peel or separate from the recording paper, compared to a magnetic toner that has a single peak in particle size distribution.

Furthermore, the present invention is characterized in that the aggregate of particles of 50 μm or less has substantially two peaks in its particle size distribution, and each of these peaks is independent as shown in Figure 1. They may be present, or they may overlap each other as shown in FIG.

Furthermore, in response to demands from various factors surrounding magnetic toner, such as the structure of the magnetic toner supply machine, supply method, and recording paper fixation properties, we created prototype magnetic toners with three peaks and magnetic toners with four peaks. , all Example 1.2
Although it showed the same tendency as Example 1.2, the effect was not as good as that of Example 1.2.

In other words, the main point of the present invention is that there are two peaks in the magnetic toner particle size distribution, and the effect thereof is also the greatest, and the effect of particle size distribution on fixing properties is As shown in FIGS. 3 and 4, in the magnetic toner fixed area, the small particle size toner 2 enters between the large particle size toners 10 as if forming a stone wall, and is tightly adhered to each other due to the fixing pressure. The fixing property is improved by firmly fixing to the recording paper 3, and the above effect (particularly the fixing property according to the finger rubbing test) is more remarkable when the particle size distribution has two peaks. If the particle size distribution has one, three or four peaks within 50 μm, the effect will be reduced.

Additionally, if there are many particles of 50 μm or more, large bumps (unevenness) will occur on the fixing surface, and if there are many particles of 5 μm or less, background fog will occur, which is undesirable from an environmental hygiene perspective, and will result in poor image quality. It is what it is.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 are diagrams showing the particle size distribution of an embodiment of the magnetic toner according to the present invention, and FIGS. 3 and 4 are cross-sectional views showing the fixing state of the magnetic toner, and FIGS. FIG.

Claims (1)

[Scope of Claims] 1. At least in a magnetic toner that is free from binder resin and magnetic material, aggregates with a particle size of 50 μm or less,
A magnetic toner for developing electrostatic images characterized by having two peaks in particle size distribution. 2 The magnetic toner exhibiting a particle size distribution of 15 μm or less and having a peak in the range of 5 to 12 μm is 50% by weight or less, and 15
The magnetic toner for electrostatic image development according to claim 1, characterized in that the magnetic toner having a particle size distribution of ~50 μm and having a peak at 25 μm to 44 μm accounts for 50% by weight or more.