JPH0618128B2 - Magnet roll manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a magnet roll including an anisotropic composite magnet containing a ferromagnetic powder and a thermoplastic resin.

2. Description of the Related Art In an image reproducing apparatus (dry type) such as an electrophotographic copying machine, a facsimile, and a printer, a magnetic developer (a two-component developer that is a mixed powder of a magnetic carrier and a toner or a one-component magnetic toner) is used. As a conveying means, a magnet roll is generally used in which a non-magnetic sleeve is provided with a permanent magnet member having a plurality of magnetic poles, and the two are relatively rotated.

There are various structures for the above magnet rolls,
For example, as described in Japanese Utility Model Publication No. 57-9798,
Using a permanent magnet member formed by fixing a long anisotropic block magnet obtained by press-forming ferrite powder in a magnetic field and then sintering it, or a cylindrical permanent magnet made of hard ferrite. Examples thereof include those using a permanent magnet member formed by being fixedly attached to a shaft (see, for example, JP-B-55-6907 and JP-B-53-47043). However, in the former case, there are problems such as an increase in the number of assembly steps and in low temperature demagnetization, while in the latter case, the sintered body has a large density of about 5 g / cm ³ and thus is heavy. There's a problem. In addition, sintered ferrite magnets generally have a problem that cracks and fractures are likely to occur during or after sintering, resulting in poor yield.

On the other hand, a kneaded product mainly composed of a ferromagnetic powder (generally ferrite powder) and a polymer compound (generally rubber or plastic material) is mainly used for extrusion molding or injection molding for the purpose of weight reduction and ease of manufacturing. A magnet roll using a so-called composite magnet, which is integrally molded into a cylindrical shape by a method and then magnetized after being solidified by cooling, has been proposed (Japanese Patent Laid-open No. Sho 61-206).
55-154707, 56-108207, 57-130407, 57-16
No. 4509, No. 52-12400, No. 55-32206, No. 56-5045
issue). In these cases, since the composite magnet has a lower concentration packing density of magnetic powder than the sintered magnet, an anisotropy process is performed in order to obtain magnetic characteristics equivalent to those of the sintered ferrite magnet.
This anisotropy step includes injection molding a kneaded product of the magnetic powder and the resin in a predetermined magnetic field.

As resins that can be used for these anisotropic composite magnets, polyethylene, polypropylene, polystyrene, polyamide, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer and the like are shown. However, it has been found that various problems occur when these resins are used for a long anisotropic magnet such as a magnet roll, especially for a long cylindrical anisotropic composite magnet.

When a polyamide resin is used, it has excellent magnetic properties, and has the advantage that the solidification rate is fast and the molding cycle can be greatly shortened.However, in the production of the long cylindrical magnet described above, the The polyamide resin, which is the base resin of the residual stress generated, cannot be absorbed due to stress relaxation and has a defect that cracks occur after molding or during a heat cycle test. Although it is technically impossible to reduce the frequency of cracking by strictly controlling the molding conditions, it is not suitable for mass production.

Further, when low density polyethylene is used, stress cracking occurs more frequently than polyamide and is not suitable.

Regarding ethylene-vinyl acetate copolymer, Japanese Patent Publication No. 52-124
No. 00 discloses an anisotropic composite magnet manufactured by using an ethylene-vinyl acetate copolymer having a vinyl acetate content of 8%, and this magnet has a disk shape of 20φ × 5 mm. Japanese Patent Office Sho 55
-32206 consists of 90-96 wt% ferrite powder (surface treated with organic silicon compound) and 10-4 wt% ethylene-vinyl acetate copolymer (vinyl acetate content 5-25 wt%). Although a direction magnet is disclosed, this magnet is used for a field magnet or the like. None of these known techniques relates to a long cylindrical anisotropic magnet for use in a magnet roll of an electrophotographic copying machine or the like. There is no discussion of the issue.

Further, JP-A-57-130407 discloses a long cylindrical anisotropic resin magnet in which ferromagnetic powders are bonded with an ethylene-vinyl acetate copolymer. However, in the case of such a long cylindrical anisotropic resin magnet, the problem of warpage of the molded body often occurs. Although the magnet roll is long and is usually housed in a sleeve, a slight warpage causes various serious problems.

It has been found that the warpage of the cylindrical composite magnet molded body often occurs in the case of insert molding in which the shaft of the magnet roll is previously inserted into the mold. It was also found that the warpage of the molded body occurs especially when molded in a magnetic field. The cause of this is not always clarified, but one of them is that when the melt of the magnetic material / EVA resin composition is injected into the mold in the magnetic field, the melt is not always uniformly filled. There is no point. Further, even under a non-uniform magnetic field, non-uniform filling of the kneaded material may occur. The uneven filling tends to cause the shaft to bend in the mold. When the molded body is taken out of the mold, the molded body is bent by the restoring force of the bent shaft. It is also considered that the residual stress in the resin composite magnet itself also contributes to bending and warping. Under the condition that warpage occurs, there is a problem that the magnetic force becomes non-uniform in the longitudinal direction of the magnet.

When the EVA resin is used as described above, the obtained long magnet has excellent thermal shock resistance, but there is a problem in dimensional stability such as warpage and bending.

Further, when using EVA resin, there is a problem that the molding time becomes long (for example, three times or more that when using polyamide resin).

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for efficiently producing a magnet roll having a long cylindrical anisotropic composite magnet without warpage.

A long anisotropic magnetic / resin composite magnet without warping uses an ethylene-vinyl acetate copolymer as a resin, and the vinyl acetate content of the copolymer is 4 to 10% by weight. It was discovered that the melt-kneaded material mainly composed of and the ferromagnetic powder can be molded by injecting it into a long mold under a magnetic field. The ethylene / vinyl acetate copolymer has a melt index (AS of 3 g / 10 min. Or more).
It was also found that the kneaded product was easy to mold when it had TMD = 1238).

Based on these findings, the present invention provides a ferromagnetic powder and ethylene.
A long anisotropic composite magnet molding mainly composed of a vinyl acetate copolymer, wherein the vinyl acetate content of the copolymer is 4 to 10% by weight, which is excellent in that there is no warp or bending. Provided is a method for manufacturing a maglet roll having a molded body having excellent magnetic properties.

Configuration of the Invention The long composite magnet of the present invention may have any cross-sectional shape, but is preferably cylindrical because it is easy to manufacture. The length / diameter ratio of the cylindrical composite magnet, when used for a magnet roll, is usually about 5 or more, but substantially about 10 or more. There is no particular limitation on the length / diameter ratio, but as the ratio increases, the problem of warping and bending becomes more serious.

It is well known that the smaller the content of vinyl acetate, the higher the hardness and softening point of the ethylene-vinyl acetate copolymer, but the present inventors have found that the hardness and softening of the ethylene-vinyl acetate copolymer. It has been discovered that the higher the point, the shorter the molding time and the better the dimensional stability, that is, the less warpage and bending. Therefore, from the viewpoint of molding efficiency and dimensional stability, an ethylene vinyl acetate copolymer having a low vinyl acetate content is advantageous. In particular
It is 10% by weight or less, preferably 8% by weight or less. If the vinyl acetate content is higher than 10% by weight, the warp of the obtained long composite magnet compact becomes too large to be used for a magnet roll. Also, the molding time becomes long. On the other hand, if the content of vinyl acetate is too low, it becomes impossible to absorb and absorb the residual stress sufficiently, and the molded product tends to crack. Therefore, it is necessary that the content of vinyl acetate is 4% by weight or more (preferably greater than 4% by weight).

Further, from the viewpoint of moldability, it is necessary that the ethylene-vinyl acetate copolymer has good fluidity, and specifically, it is necessary that it has a melt index of 3 g / 10 min or more.

Commercially available ethylene vinyl acetate copolymers usable in the present invention include M-2030 (vinyl acetate content 6% by weight, melt index 70 g / 10 mi, manufactured by Mitsui Polychemicals).
n) and P-0607 (vinyl acetate content 6% by weight, melt index 25 g / 10 min), Sumitomo Chemical D-30
21 (vinyl acetate content 6% by weight, melt index 7
g / 10 min), NUC-5491 manufactured by Nippon Unicar (vinyl acetate content 6% by weight, melt index 5.5 g / 10 min)
And so on.

In the present invention, as the ferromagnetic powder, Ba ferrite,
Ferrite powder having magnet-plumbite type crystal structure such as Sr ferrite, alnico magnet powder, Fe-
Ferromagnetic powders such as Cr—Co based magnet powder, rare earth cobalt magnet powder, and rare earth iron magnet powder can be used.
The blending amount of these ferromagnetic powders may be determined so that the weight ratio of ferromagnetic powder: resin is 80 to 96:20 to 4, preferably 85% by weight or more of magnetic powder. When the blending amount of the ferromagnetic powder is less than 80 parts by weight, it is difficult to obtain a predetermined magnetic property (the residual magnetic flux density on the magnet surface is 1400 G or more), and when the blending amount exceeds 96 parts by weight, molding becomes almost difficult. The surface of the ferromagnetic powder may be previously coated with an organic silicon compound, an organic titanate compound or the like in order to improve the wettability with the resin.

In addition to the magnetic powder and resin, a small amount (several weight%) of a lubricant such as polyethylene wax, calcium stearate, or an acid amide compound may be added to improve moldability.

According to the present invention, an elongated composite magnet having anisotropy can be obtained using the above raw materials as follows. First, a kneaded material containing ferromagnetic powder, EVA resin, and other additive materials as needed is prepared. Next, the kneaded product is poured into a mold provided with an electromagnet or a permanent magnet on the periphery, injection molding is performed while heating while applying a magnetic field, and after cooling and solidification, a molded product is taken out from the mold. 6000-
It is suitable to mold in a magnetic field of about 10,000 G. The anisotropy treatment can be performed so as to provide an arbitrary number of magnetic poles according to a desired application. From the viewpoint of downsizing and simplification of equipment, it is advantageous to perform injection molding in a magnetic field of a permanent magnet. The molded body thus obtained can be used for a magnet roll without further processing, but the outer shape may be processed into a predetermined dimension as necessary.

When producing a long composite magnet for a magnet roll, it is convenient to make the molded body into a cylindrical shape, but this can be achieved by simply using a cylindrical mold. A magnet roll can be created by attaching a shaft to a cylindrical magnet.

The magnet roll can also be made in one step by insert molding. In this case, the shaft is previously inserted into the cylindrical mold, and the kneaded material is injected while applying a magnetic field. Since the molded body has the composite magnet and the shaft integrated, it can be used as it is as a magnet roll.

The obtained magnet roll is magnetized in the same direction as the anisotropic direction, housed in an appropriate sleeve, and then mounted in a developing device or the like.

EXAMPLES AND COMPARATIVE EXAMPLES OF THE INVENTION Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 8.90 kg of Sr ferrite powder having an average particle size of 1.60 μm was added to ethylene vinyl acetate copolymer (Mersen 900 manufactured by Toyo Soda Co., Ltd., vinyl acetate content 4% by weight, melt index 30 g / 10 min) 1.10
Kg was added and the mixture was kneaded by a twin-screw extruder at a temperature of 130 ° C.
The resulting fluid kneaded product was used for the magnet roll shaft (outer diameter
10mmφ, sus304) standing injection molding machine equipped with an injection temperature 230 ℃, injection pressure 1200kg / cm ² , injection time 6sec,
Injection was performed under the conditions of a mold temperature of 80 ° C. and a cooling time of 70 seconds. The magnetic field was applied so that the magnetic poles of the molded body had three NSS poles.
Then, after cooling and solidification, a molded body with a shaft (outer diameter 28 mmφ, length 240 mm) was taken out from the mold. Then, 10 molded bodies were manufactured under the same conditions.

Example 2 M-2030 as an ethylene-vinyl acetate copolymer (Mitsui Polychemical, vinyl acetate content 6% by weight, melt index
10 g under the same conditions as in Example 1 except that 7 g / 10 min) was used.
A molded body of a book was produced.

Example 3 P-0607 as an ethylene vinyl acetate copolymer (manufactured by Mitsui Polychemical, vinyl acetate content 6% by weight, melt index
10 g under the same conditions as in Example 1 except that 25 g / 10 min) was used.
A molded body of a book was produced.

Example 4 As ethylene vinyl acetate copolymer (Sumitomo Chemical Co.,
Vinyl acetate content 6% by weight, melt index 7g / 10min)
Ten molded bodies were manufactured under the same conditions as in Example 1 except that was used.

Example 5 NUC-5491 as an ethylene vinyl acetate copolymer (manufactured by Nippon Unicar, vinyl acetate content 6% by weight, melt index)
1) under the same conditions as in Example 1 except that 5.5 g / 10 min) was used.
0 molded bodies were produced.

Example 6 NUC-3140 (manufactured by Nippon Unicar, vinyl acetate content 10% by weight, melt index as ethylene vinyl acetate copolymer)
Ten compacts were manufactured under the same conditions as in Example 1 except that 20) was used.

Comparative Example 1 1.50 kg of nylon 6 (1011FB manufactured by Ube Industries) was added to 8.50 kg of Sr ferrite powder having an average particle size of 1.47 μm by a twin-screw extruder.
Kneading was performed at a temperature of 240 ° C. Next, 10 molded bodies were manufactured under the same conditions as in Example 1 except that the obtained kneaded product was molded at an injection temperature of 280 ° C. and an injection pressure of 900 kg / cm ² .

Comparative Example 2 Ten molded products were manufactured under the same conditions as in Example 1 except that low density polyethylene (Mirason 68 manufactured by Mitsui Polychemical) was used instead of the ethylene-vinyl acetate copolymer.

Comparative Example 3 Evaflex P-1207 manufactured by Mitsui Polychemicals as an ethylene-vinyl acetate copolymer (vinyl acetate content 12% by weight,
Ten compacts were manufactured under the same conditions as in Example 1 except that the melt index was 12 g / 10 min).

Comparative Example 4 Ten molded products under the same conditions as in Example 1 except that Evaflex 410 (vinyl acetate content 19% by weight, melt index 400 g / min) manufactured by Mitsui Polychemical was used as the ethylene-vinyl acetate copolymer. Was produced.

Comparative Example 5 H-4011 manufactured by Sumitomo Chemical Co., Ltd. as an ethylene-vinyl acetate copolymer
(Vinyl acetate content 20% by weight, melt index 20g
/ 10 min) was used to produce 10 compacts under the same conditions as in Example 1.

For the molded body obtained in each of the examples and comparative examples,
The presence or absence of cracks in the molded body, warpage, thermal shock resistance by a heat cycle test, density and magnetic properties after magnetization were measured. The results are shown in Table 1. Table 1 also shows the required molding time for each molded body. In the heat cycle test, as shown in Fig. 1, the sample was heated from room temperature to 40 ° C at a rate of 2 ° C / minute (section AB), kept at 40 ° C for 3 hours (BC), and 2 ° C / minute. At a cooling rate of -40 ° C (C-D), kept at -40 ° C for 3 hours (D-E), and again 2
A (EF) cycle of heating to room temperature at a rate of ° C / min was repeated 5 times.

As is clear from Table 1, the molded products obtained in Examples 1 to 6 have sufficiently satisfactory results in terms of magnetic properties, thermal shock resistance and dimensional accuracy, and have good molding efficiency. .

FIG. 2 shows the magnetic flux density distribution in the circumferential direction of the molded body having three NSS magnetic poles obtained in Example 1.

On the other hand, the polyamide-containing molded body of Comparative Example 1 has good magnetic properties and molding efficiency, but as shown in FIG. 3, it is considered that the residual stress is caused in the cylindrical permanent magnet 1 fixed to the shaft 2. Many possible stress cracks 3 tend to occur and the molding yield is significantly low. Also, when the polyethylene of Comparative Example 2 is used, cracking is severe. Comparative Example 3
It can be seen that the molded product of No. 5 is extremely inferior in dimensional accuracy and molding efficiency.

As described above, according to the present invention, by using an ethylene vinyl acetate copolymer having specific properties as a base resin, magnetic properties excellent in magnetic properties, dimensional stability and thermal shock resistance can be obtained. The long cylindrical composite magnet can be efficiently obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing heat cycle conditions, FIG. 2 is a diagram showing a magnetic flux density distribution of a composite magnet obtained by the method of the present invention, and FIG. 3 is a perspective view of a molded body obtained by the conventional method.

Front page continued (72) Inventor Chitoshi Hagi 5200 Mikkajiri, Kumagaya, Saitama Prefecture Inside the Hitachi Metals Co., Ltd. Kumagaya Plant (72) Inventor Satoru Koizumi 5200, Mikkajiri, Kumagaya, Saitama Inside Kumagaya Plant 56) References JP-A-57-130407 (JP, A) JP-B 52-12400 (JP, B1) JP-B 55-32206 (JP, B2)

Claims (1)

[Claims] 1. A ferromagnetic powder and vinyl acetate content of 4-10.
In wt%, melt index (ASTM D123
8) is mainly composed of an ethylene-vinyl acetate copolymer having a content of 3 g / 10 min or more, and the ferromagnetic powder and the ethylene-
A mixture containing a vinyl acetate copolymer in a weight ratio of 80 to 96:20 to 4 is fluidized, and has a cylindrical molding space having a length / diameter ratio of 5 or more in the presence of a magnetic field, and the shaft is A method for producing a magnet roll, comprising performing injection molding in an inserted mold, and magnetizing the outer peripheral surface of the obtained cylindrical molded body with a shaft in multiple directions in the same direction as the anisotropic direction.