JPH07113782B2 - Thermal roll fixing type magnetic toner for developing magnetic latent image - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic toner for developing a magnetic latent image capable of fixing with a heating roll, which is used in a magnetic printing system.

[Conventional technology]

As one of the image reproducing methods, a magnetic printing method applying a magnetic recording technology has been developed and put into practical use. The magnetic printing method includes a step of writing an information signal on a magnetic drum which is a recording medium by a magnetic head to form a magnetic latent image, and a step of developing the magnetic latent image with a one-component magnetic toner,
It includes a step of transferring the toner image onto the transfer sheet, a step of fixing the transferred toner image, and a step of cleaning the magnetic toner remaining on the magnetic drum after the transfer.
(See JP-A-54-32328 and JP-A-55-108681) This magnetic printing method does not require replacement of the photoconductor for every tens of thousands of copies unlike the electrophotographic method, and is easy to maintain. Have.

The fixing method in the magnetic printing method is performed by a heat roll fixing method, an oven fixing method, a flash lamp fixing method or a pressure fixing method as in the electrophotographic apparatus. Among them, in the heat roll fixing method, since the surface of the heating roll and the toner image supporting surface on the substrate to be fixed are in pressure contact with each other, the thermal efficiency at the time of fusing the toner image on the substrate is high, and high speed fixing (300 mm It has the advantage that it can be more than sec).

[Problems to be solved by the invention]

In the above magnetic printing method, a part of the magnetic force lines generated by energizing the magnetic head leaks from the gap of the magnetic head to the recording medium to form a magnetization pattern (latent image). Therefore, it is preferable that the gap between the magnetic head and the magnetic drum is as narrow as possible, generally 5 μm or less (practically about 1 μm), which is extremely narrow.

However, when a magnetic toner mainly composed of a thermoplastic resin such as a styrene resin and magnetic powder and capable of being fixed by a heat roll is used, a phenomenon occurs in which the toner adheres to the magnetic head.

More specifically, when writing information on the magnetic drum by the magnetic head, the cleaning blade is separated from the magnetic drum, so that the toner accumulated at the tip of the blade scatters and adheres to the magnetic head. Since the heat roll fixing type toner has a property of being easily melted by heat, it is in a state of being fused to the magnetic head and is not easily separated. Even if the blade is cleaned, some toner remains on the magnetic drum. When the information signal is written, the magnetic head also scans the magnetic drum, so that the toner adheres to the magnetic head. Thus, the amount of toner adhered to the magnetic head increases as the number of times the magnetic head writes the information signal increases. When the magnetic head is contaminated due to toner adhesion, the gap between the magnetic drum and the magnetic head is apparently widened, so the potential of the magnetic latent image is lowered, that is, the force for attracting the magnetic toner is weakened. Image density is reduced. In particular, the recording speed may be extremely high at 100 sheets per minute (A4 size) in a machine using heat roll fixing, so this problem becomes more and more serious when continuously obtaining images.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thermal roll fixing type magnetic toner which can reduce the contamination of the magnetic head and can obtain a high density image.

[Means for solving problems]

The magnetic toner of the present invention is a magnetic toner used in a magnetic printing system in which a magnetic latent image is transferred after development and then subjected to heat roll fixing to obtain a final image, which is a toner particle containing a thermoplastic resin and magnetic powder. 1,500 to 12,000 on the surface of
The polyethylene resin having a molecular weight in the range is fixed.

As a result of various studies to prevent the magnetic head from being soiled in the magnetic printing system, the present inventor has found that it is effective to fix the polyethylene resin on the surface of the fixing resin and the toner particles containing the magnetic powder.

When a magnetic latent image is developed using a magnetic toner with a polyethylene resin adhered to its surface, the toner temporarily adheres to the magnetic head, but since polyethylene has the property of shrinking after cooling, it easily peels off. , No longer adheres to the magnetic head.

The polyethylene resin that adheres to the surface of the toner particles is 1,50
It is necessary to have a molecular weight in the range 0 to 12,000.
When the molecular weight is less than 1,500, the polyethylene becomes too soft and the toner is apt to agglomerate, resulting in deterioration of storage stability. If the molecular weight exceeds 12,000, the polyethylene becomes hard and it becomes difficult to fix the toner.

Such polyethylene is used per 100 parts by weight of toner particles
It is desirable to fix the toner particles on the surface of the toner particles in the range of 0.1 to 5 parts by weight. If the adhered amount is less than 0.1 parts by weight, the effect is small, and if the adhered amount exceeds 5 parts by weight, the fixability may be deteriorated or offset due to the heat roll may occur. Further, polyethylene may be added to the inside of the toner particles, whereby the adhesion to the magnetic head can be further prevented.

Next, the toner particles contain a fixing resin and magnetic powder as essential components.

As the fixing resin, it is desirable to use a styrene resin having a Tg of 50 ° C. or higher, a polyester resin, an epoxy resin, and a mixed resin thereof in order to enable fixing by a hot roll. Although there are various styrene resins, styrene-acrylic copolymers and styrene-butadiene copolymers are preferable from the viewpoint of fixability and offset resistance, and styrene-acrylic copolymers are more preferable. Examples of the styrene-acrylic copolymer include a styrene monomer, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-chloro-ethyl acrylate, and acrylic. Α-methylene aliphatic monocarboxylic acid esters such as phenyl acid ester, methyl α-chloroacrylate, methyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, β-hydroxyethyl methacrylate, glycidyl methacrylate, diethylaminoethyl methacrylate Copolymers with a group such as styrene-acrylate copolymer and styrene-methacrylate copolymer can be effectively used.
Further, as the polyester resin, one or more polyols and one or more polyols are also used from the viewpoint of fixing property and offset resistance.
A non-linear polyester resin produced from one or more dicarboxylic acids is desirable.

As the magnetic powder, an alloy or a compound containing an element exhibiting ferromagnetism such as ferrite, magnetite, etc., such as iron, cobalt, nickel, etc. can be used. Is good. The content of the magnetic powder is suitably in the range of 40 to 75% by weight. If it is less than 40% by weight, the magnetic force of the toner is weakened so that the toner is easily separated from the sleeve, fog is increased, and the transportability is deteriorated. If it exceeds 75% by weight, the fixability is lowered.

In addition to the above components, the toner particles of the present invention may be added with compounds such as low molecular weight polyolefin, fatty acid metal salts, fatty acid esters and partially saponified products thereof in order to enhance the offset prevention effect. Low molecular weight polypropylene is the most common. Besides this,
Toner particles containing one or more known additives such as a fluidity modifier (for example, hydrophobic silica), conductive particles (for example, carbon black), and a charge control agent (for example, nigrosine dye, synthetic metal azo dye). May be added to the inside and / or the surface. The addition amount is appropriately 10% by weight or less so as not to impair the fixability.

The magnetic toner of the present invention can be manufactured, for example, as follows.

First, a fixing resin and raw materials containing magnetic powder are dry-mixed, kneaded by heating, cooled and solidified, and then pulverized. The obtained pulverized powder is heat-treated and then classified to obtain toner particles having a predetermined particle size.

Next, the toner particles and the granular polyethylene resin are dry-mixed to obtain a magnetic toner in which the polyethylene resin is fixed on the surface of the toner particles.

The magnetic toner of the present invention preferably has a volume resistance of 10 ¹⁴ Ω · cm or more in order to facilitate transfer to plain paper. This resistance value is obtained by measuring a small amount of sample (tens of mg) and improving the dial gauge to an inner diameter of 3.05 mm (cross-sectional area = 0.073c).
It was filled in an insulating cylinder made of Teflon (trade name) of m ² ), applied with a load of 0.1 kg, and measured with an electric field of D.C4 KV / cm. A Yokogawa Hewlett-Packard insulation resistance meter (4329 A type) was used for the measurement.

Further, the magnetic toner of the present invention preferably has a charging voltage within ± 25 V in order to reduce fog. This charging voltage (surface potential) is measured by the device shown in FIG. In the figure, 1 is a non-magnetic sleeve (outer diameter 50 mm
φ), 2 is a permanent magnet member (outer diameter 46 mm, length 150 mm, 12-pole symmetrical magnetization, magnetic flux density on the sleeve 1000 G), 3 is a surface electrometer (Trek 344), and 4 is a probe. After adjusting the gap g between the sleeve 1 and the probe 4 to 5 mm,
3 g of toner is supplied onto the sleeve 1, and the permanent magnet member 2 is
The surface potential of the toner is measured when the toner is rotated at 000 rpm for 1 minute.

〔Example〕

Hereinafter, details of the present invention will be described by way of examples, but the present invention is not limited to these examples.

Example 1 Styrene-acrylic copolymer (Mw = 16,000, Mn = 6,600)
35 parts by weight and 65 parts by weight of magnetite (EPT500 manufactured by Toda Kogyo Co., Ltd.) were dry-mixed and kneaded at a temperature of 100 ° C. with Banbury. The kneaded product was cooled and solidified, then pulverized with a jet mill into particles of 20 μm or less, and classified to obtain toner particles having an average particle size of 15 μm. By adding and mixing particles of medium density polyethylene wax (molecular weight 4,000) to the toner particles, a magnetic toner (No. 1) having 0.2 parts by weight of polyethylene wax fixed on the surface of the toner particles was obtained.

The volume resistance of this magnetic toner is 1 × 10 ¹⁵ Ω · cm,
The charging voltage on the sleeve was -12V.

Example 2 Example 1 except that the amount of polyethylene wax added was changed.
Four types of magnetic toners (Nos. 2 to 5) were manufactured under the same conditions as described above. The amount of polyethylene wax adhered was 0.5 parts by weight of the No. 2 toner, 1 part by weight of the No. 3 toner, 3 parts by weight of the No. 4 toner, and 5 parts by weight of the No. 5 toner.

Example 3 Styrene-acrylic copolymer (Mw = 25,000, Mn = 36,00
0) 30 parts by weight, magnetite (EPT500 manufactured by Toda Kogyo) 68 parts by weight, high-density polyethylene wax (molecular weight 8,000) 2
Parts by weight were dry mixed and kneaded at a temperature of 100 ° C. with Banbury. After the kneaded material is cooled and solidified, it is 20 μm in a jet mill.
The following particles were pulverized and classified to obtain toner particles having an average particle size of 15 μm. By adding low-density polyethylene wax (molecular weight 2,000) particles to the toner particles and mixing them, a magnetic toner (No. 6) having 2 parts by weight of polyethylene wax fixed on the surface of the toner particles was obtained.

The volume resistance of this magnetic toner is 1 × 10 ¹⁵ Ω · cm,
The charging voltage on the sleeve was -12V.

Comparative Example 1 A magnetic toner (No. 7) was obtained under the same conditions as in Example 1 except that polyethylene wax was not added to the surface of the toner particles.

Comparative Example 2 A magnetic toner (No. 6) was prepared under the same conditions as in Example 1 except that 6 parts by weight of polyethylene wax was added to the surface of the toner particles.
8) got.

Continuously using the above magnetic toner under the following conditions 1
Ten thousand images were evaluated.

A magnetic drum (outer diameter 250 mm) having a Co-Ni layer formed on an aluminum alloy drum was rotated at a peripheral speed of 150 mm / sec, and an image was written by a magnetic head to form a magnetic latent image. Inside a stainless steel sleeve with an outer diameter of 50 mm, a barium ferrite magnet with an outer diameter of 48 mm (4-pole magnetized,
The magnetic flux density on the sleeve was 60 G for the developing magnetic pole, and 500 G for others). The magnetic latent image was developed by a developing device equipped with a magnet roll. Here the doctor gap is 0.8m
m, the developing gap was set to 0.6 mm, and the sleeve was rotated at 80 rpm in the same direction as the magnetic drum in the developing section. The toner image obtained as a result of development was corona-transferred onto plain paper at a transfer voltage of 6 KV. The plain paper bearing the transferred toner image is passed between a heat roll whose surface is heated to 180 ° C [the surface is coated with Teflon (trade name)] and an RTV silicone rubber roll (pressure between the rolls is 1 kg. / cm), the final image was obtained.
The image evaluation results are shown in Table 1.

As shown in Table-1, with the magnetic toner (No. 1 to 6) in which the polyethylene wax having a specific molecular weight is fixed on the surface of the toner particles in the range of up to 5 parts by weight, the magnetic head becomes dirty even after continuous printing of 10,000 sheets. It can be seen that the image density is extremely small and a high image density can be obtained. On the other hand, with the magnetic toner (No. 7) to which polyethylene wax is not added, the magnetic head is heavily soiled and the image density is reduced. In addition, the magnetic toner (No. 8) containing a large amount of polyethylene is inferior in fixability.

〔The invention's effect〕

As described above, in the magnetic toner of the present invention, since polyethylene wax is added to the surface of the toner particles, the magnetic head is less contaminated even in continuous printing, and a high quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a toner surface potential measuring device.

Claims (1)

[Claims] 1. Polyethylene resin particles having a molecular weight in the range of 1,500 to 12,000 are added to the surface of toner particles containing a thermoplastic resin and magnetic powder in an amount of 0.1 to 100 parts by weight of the toner particles.
A magnetic toner for magnetic latent image development of a heat roll fixing type, characterized in that 5 parts by weight are fixed.