KR19980028387A - Binder for producing resin bond magnets, compositions containing the same, and methods for producing resin bond magnets - Google Patents

Abstract

The present invention is a binder for preparing a resin bond magnet comprising four components of polypropylene (polypropylene or PP), ethylene propylene (ethylenepropylene or EP), ethylene vinyl acetate (ethylenevinylacetate or EVA), and high density polyethylene (HDPE). The present invention relates to a composition for producing a resin bond magnet, and a method for producing the same. Filling the binder according to the present invention with a high density of magnetic material to increase the magnetic properties, as the main material of the binder by using a polypropylene excellent in flowability and excellent machinability, the seed fluidity, thermal stability, Laser beam prints, copiers, DC motors that require uniform and precise magnetic properties and dimensional accuracy by injection and extrusion molding that can solve all the conventional problems such as water absorption by resin, deformation by shrinkage after molding, and post-processing after molding. Provides a highly functional resin bond magnet used for the back.

Description

Binder for producing resin bond magnets, compositions containing the same, and methods for producing resin bond magnets

The present invention relates to a binder used to prepare anisotropic (or multipolar anisotropic) resin bond magnets by injection molding in a magnetic field, a resin bond magnet composition in which magnetic powder is mixed with the binder, and a method of preparing a resin bond magnet using the composition. It is about.

The resin bond magnets thus manufactured are used in laser beam printers (LBPs), copiers, DC motors, and the like.

Generally, a mixture of magnetic powder and a binder is used to prepare a resin bond magnet.

Japanese Patent Laid-Open No. 5-109516 describes a polyamide resin and a polyamide copolymer binder as a binder mixed with magnetic powder.

Polyamide-based resins have a high shrinkage upon cooling (the heat swelling coefficient of nylon is 10 ^-1 cm 3 / mol K.), so that when the mixture using this resin is cooled after hot melt injection molding, it is deformed into the molded body by shrinkage. This occurs and causes warpage in the longitudinal direction, particularly in the production of long shaped bodies. In addition, the polyamide-based resin has a hydrophilic polar group in the molecular structure has a high water absorption rate has a disadvantage that it is difficult to obtain a uniform surface flux density due to the generation of pores (pore) during the melt injection molding process.

When nylon-6 is used as the binder, the water absorption at room temperature and 100% relative humidity is 10.5%. When nylon-66 is used as the binder, the water absorption is 8% under the same conditions as above.

Figure 1 shows the change in the powder anisotropy according to the change of the applied magnetic field during injection of the nylon composition, where the nylon composition refers to a mixture of nylon resin and ferrite magnetic powder. As can be seen from this figure, even when the magnetic field strength is 8 kOe, the anisotropy is not achieved in about 85%, and as can be seen in FIG. 7, the water absorption of the nylon composition is considerably high compared to other compositions. Therefore, as can be seen from Figures 1 and 7, the nylon composition is not able to obtain the desired surface magnetic flux density.

In addition, when a resin bond magnet was manufactured using a crosslinked polyphenylenesulfide (PPS) -based polymer as a binder, the resin bond magnet produced had a low water absorption rate but was very poor in impact resistance. When used in the magnet roller, which is a long product, after machining by lathe machining, the machinability of the resin is poor and excessive force is applied to the cutting surface, which may cause bending in the longitudinal direction.

In addition, when rubber is used as a binder, it is difficult to produce resin bond magnets requiring precise magnetic properties because high anisotropy of magnetic powder cannot be obtained due to the high melt viscosity of the resin.

Therefore, the present invention is to reduce the fluidity, thermal stability, deformation of the molded body by shrinkage, poor impact resistance, water absorption, In order to solve the problems such as machinability difficulties during processing, and to achieve a high anisotropy, to produce a resin bond magnet having a uniform surface magnetic flux density.

More specifically, when manufacturing anisotropic (or multipolar anisotropic) resin bond magnets having high and uniform surface magnetic flux density by high anisotropy, high anisotropy can be obtained by using anisotropic magnetic powder, and the magnetic field strength of magnetic field injection machine is changed. It can be achieved, but the achievement of high anisotropy by this method has some problems. First, there is a limit to increase the magnetic field strength of the magnetic field injection machine using magnetic powder, and secondly, the non-uniform magnetic field strength in the magnetic field injection machine can cause the nonuniformity of the surface magnetic flux density of the molded body.

Therefore, the polypropylene (PP-141, manufactured by PP, DAELIM POLY (KOR)) having a high melt index improves the anisotropy of the resin bond magnets manufactured and the impact resistance of the polypropylene. Ethylene propylene (EP, ethylene propylene copolymer, trade name BJ800 manufactured by SAMSUNG GENERAL CHEMICALS (KOR)), ethylene vinyl acetate (EVA, ethylene vinyl acetate random copolymer, trade name HE10 manufactured by SUMITOMO (JAP) After mixing high density polyethylene (HDPE, brand name J520A manufactured by SAMSUNG GENERAL CHEMICALS (KOR)) with a binder mixed with polypropylene and magnetic powder, it is made into pellets and injected at a magnetic strength of 2 to 10 kOe depending on the characteristics of the magnetic powder. To prepare a resin bond magnet having a uniform surface magnetic flux density.

Therefore, in the present invention, the machinability is good, there is no deformation and warpage in the longitudinal direction due to shrinkage during cooling, good impact resistance, not too high moisture absorption, and high anisotropy of the magnetic powder can be obtained due to the moderate melt viscosity. It is to prepare a composition for producing a resin bond magnet having precise magnetic properties and a resin bond magnet using the composition.

1 is a view showing the change in powder anisotropy (injection temperature 260 ℃) according to the change of the applied magnetic field during injection of the nylon composition.

Figure 2 shows the change of the residual magnetic flux density according to the change of the applied magnetic field during injection (magnetic powder content of 87wt.%, Binder composition A / B / C / D = 40/15/10/35, injection temperature 240 ℃, where A = Polypropylene, B = ethylene propylene, C = high density polyethylene, D = ethylene vinyl acetate).

Figure 3 is a view showing the change in the powder anisotropy (magnetic powder content 87wt.%, Binder composition A / B / C / D = 40/15/10/35, injection temperature 240 ℃) according to the change of the applied magnetic field during injection .

4 is a view showing the change of powder anisotropy according to the change of applied magnetic field during injection (magnetic powder content 82wt.%, Binder composition A / B / C / D = 40/15/10 // 35, injection temperature 240 ℃) Shown.

5 is a view showing a change in powder anisotropy (binder composition A / B / C / D = 40/15/10/35, injection temperature 240 ℃) according to the change in the magnetic powder content.

6 is a change of the sum of the residual magnetic flux density in the parallel and vertical direction of the applied magnetic field according to the change of magnetic powder content (usable magnetic powder: strontium ferrite magnetic powder, binder composition A / B / C / D = 40/15/10/35 , Injection temperature 240 ℃).

7 is a view showing the water absorption of each binder over time in 50 ℃ water.

8 is a view showing a change in viscosity at each shear rate with a change in temperature of the composition.

9 is a view showing the viscosity change (shear rate 542 sec -1) according to the magnetic powder content change.

Figure 10 shows the change in viscosity (A / B / C / D = 40 / 50-X / 10 / X, shear rate 1625 sec-1) according to the amount of D resin added in the A / B / C / D binder drawing.

FIG. 11 shows the powder anisotropy according to the change in the amount of D resin added in the A / B / C / D binder (A / B / C / D = 40 / 50-X / 10 / X, applied magnetic field of 4 kOe and 8 kOe). Drawing showing change.

The binder for the resin bond magnet is composed of four components such as polypropylene, ethylene propylene, ethylene vinyl acetate, and high density polyethylene. The binder was composed of 30 to 95 wt.% Polypropylene, 5 to 20 wt.% Ethylene propylene, 10 to 40 wt.% Ethylene vinyl acetate, and 5 to 20 wt.% High density polyethylene when the total content of the binder was 100 wt.%. . Preferably, when the composition of the binder is 40 wt.% Polypropylene, 15 wt.% Ethylene propylene, 35 wt.% Ethylene vinyl acetate, 10 wt.% High density polyethylene, a resin bond magnet having a high anisotropy and a uniform surface magnetic flux density is obtained. Lose.

Polypropylene is the main component of the components constituting the binder, and determines the main physical properties such as strength and thermal properties of the binder. Toughened ethylene vinyl acetate and high-density polyethylene were added to compensate for the weak physical properties, which are disadvantages of polypropylene. Thus, ethylenevinylacetate, high density polyethylene, acts as a modifier. The most problematic problem when mixing such polymers is that the compatibility between each polymer component is low, resulting in phase separation. At this time, it is difficult to expect effective improvement of physical properties because the bonding strength between the polymers is weak at the interface. Therefore, a compatibilizer is used to improve the physical properties by improving the bonding force at the interface between different phases, and generally a block copolymer is used. For this reason ethylene propylene copolymers are selected.

More specifically, the components of the binding agent for the resin bonded magnet of polypropylene (heat gwaengchang coefficient 10 ^-2 ㎤ / mol K) is for high anisotropic ratio of the powder flowability is excellent, the non-polar molecular structure for the low water absorption It was selected to prevent excessive dimensional deformation due to shrinkage after molding by injection or extrusion and warping of the molded body. In addition, polypropylene is used as the main binder to determine the process temperature of the resin-bonded magnet molding composition and have a major influence on the mechanical strength of the molded article. Ethylene vinyl acetate copolymer was added to improve impact strength by absorbing shock and generating crazy by forming a rubber phase evenly dispersed in polypropylene. High-density polyethylene was added to reduce the softening of the seed-producing material as the composition for resin bond magnets would contain many rubbery phases. Ethylene propylene block copolymer was added for improving the compatibility between the crystalline phase and the rubber phase to improve the bonding strength between the resin-bonded magnet composition and effective impact strength improvement effect.

In general, in the case of injection molding of a composite, the selection of a resin having a high melt index (MI) is good for the high anisotropy of the powder, and the selection of the resin having a high degree of crystallinity is good in view of the mechanical strength of the resulting molded body.

On the other hand, amorphous resins are generally better for use in extrusion molding.

In determining the composition between each component, it is determined in consideration of mechanical properties and rheological intellectual properties. Polypropylene occupies most of the composition since it is the main component of the binder. However, at low compositions of ethylene propylene, high density polyethylene, and ethylene vinyl acetate, it is difficult to expect effective brittleness improvement. Therefore, it is preferable to determine the composition of polypropylene at about 40 wt.% In the binder, and then change the composition of other components. On the other hand, when the addition amount of the high density polyethylene in the binder is 10wt.% Or more, the melt flowability of the binder is drastically reduced, and the anisotropy rate of the magnetic powder is inadequate. Therefore, the composition of the high density polyethylene in the binder was determined to be 10wt.%, And the changes in the mechanical properties and rheological properties of the ethylene vinyl acetate and ethylene propylene were investigated. At this time, when the composition of polypropylene 40wt.%, Ethylenepropylene 15wt.%, Ethylene vinyl acetate 35wt.%, High density polyethylene 10wt.%, The flowability and mechanical properties of the binder are excellent, and high anisotropy is achieved to achieve uniform surface magnetic flux density. It is possible to obtain a resin bond magnet having.

Referring to Figure 10 it can be seen that the viscosity of the binder significantly increases in the content of 20wt.% To 30wt.% Of ethylene vinyl acetate, and then rapidly decreases from 30wt.% To 35wt.% And then increases again. Therefore, if it is desired to improve the fluidity of the composition, it can be said that it is desirable to add about 35wt.%. Even at 20wt.%, The viscosity is lower than 35wt.%, But when this content is used, the toughness after molding tends to be somewhat reduced. 11 also shows the highest anisotropic rate at 35wt.% Of ethylene vinyl acetate. Therefore, in the following drawings, 35 wt.% Of ethylene vinyl acetate in the composition was used to show the relationship between the magnetic powder content, the magnetic field strength, and the anisotropy rate.

In addition, additives such as plasticizers, stabilizers, lubricants, and surface treatment agents may be added to the binder. Commonly used molding aids, lubricants, lubricants, and the like can be added, and lubricants include stearic acid, stearic acid salts, fatty acid amides, waxes, and lubricants. Such a molding agent is preferably about 0.05 to 0.5 wt.% Based on the mixture of the magnetic material and the mattress resin.

The composition for the resin bond magnet consists of the binder and the magnetic powder.

The composition of the composition is preferably 9 to 30 wt.% Binder and 70 to 91 wt.% Magnetic powder when the total content of the composition is 100 wt.%.

In fact, when the content of the inorganic powder falls below the above range, the magnetic properties of the resin bond magnets are reduced, and when the content of the inorganic powder is 92 wt.% Or more, the viscosity increases, so that the orientation of the magnetic powder is reduced during the uniform mixing process and injection molding during the magnetic field. Or, the injection process itself is difficult disadvantages. Therefore, in more detail, the composition of the composition is preferably composed of 13wt.% Binder and 87wt.% Magnetic powder.

5 is a view showing the change of powder anisotropy according to the change of magnetic powder (strontium-ferrite) content is constant at the content of the magnetic powder of 87wt.% Or less, it can be seen that the anisotropy rate is rapidly decreased at 87% or more. have.

Magnetic material powder used in the present invention means a magnetic material capable of magnetizing. Therefore, the magnetic material powder may be magnetized by applying a magnetic field at the time of manufacture or after the manufacture of the magnet even if it is not magnetized itself. As such magnetic powder, ceramic powder and alloy powder may be used. Specifically, anisotropic strontium ferrite magnetic powder, which is a kind of ceramic powder, anisotropic samarium-cobalt magnetic powder, which is a kind of rare earth alloy, and anisotropic neodymium which is a kind of rare earth alloy Iron-boron magnetic powder can be used. The magnetic powder used should have an average particle size of 0.8 ~ 5㎛ which is anisotropic.

Next, as described above, the method for producing a resin bond magnet in the injection molding process in the magnetic field using the composition of the present invention will be described in detail.

Before mixing the binder in the magnetic powder and the mixer, the surface of the magnetic powder is coated with a silane coupling agent corresponding to 0.1 to 1.0 wt.% Of the magnetic powder in order to increase the bonding strength of the organic binder and the inorganic powder. The type of silane coupling agent used at this time is A-1100, A-1170, A-186, A- manufactured by UNION CARBIDE CHEMICALS AND PLASTICS COMPANY INC. 187, A-174, A-171, A-172, UCARSIL One of RC-1 is selected.

The coating method mixes in a mixer while spraying a magnetic powder with a solution of ethyl alcohol and a coupling agent in a weight ratio of 3: 1. At this time, the temperature of the mixer is mixed while maintaining the temperature of 50 ~ 80 ℃, the surface coating by removing the residual alcohol remaining in the powder after mixing in a dry oven of 80 ~ 100 ℃.

Thus, the surface-coated magnetic powder and a binder composed of a multicomponent system were mixed to provide fluidity and formability. When the total content of the composition was 100 wt.%, The binder was 8-30 wt.% And the magnetic powder was 70-92 wt.%, And mixed in a mixer in a temperature range of 160-200 ° C. At this time, the mixture was first mixed in a Z-blade mixer and then effectively mixed using an extruder. The sample pelletized by mixing the inorganic powder and the organic binder is injection molded in the temperature range of 170 ~ 250 ℃ in the magnetic field injection machine.

Referring to FIG. 8, the viscosity rapidly decreases at a temperature of about 220 ° C. to 240 ° C., and then gradually decreases at a temperature of less than 240 ° C. FIG. Decomposition of the binder may occur at temperatures above 250 ° C., so above this temperature no desirable results are obtained. Therefore, injection molding at a temperature of about 240 ℃ can improve the fluidity of the composition is preferred.

Also, referring to the relationship between the magnetic powder content, the magnetic field strength and the anisotropy with reference to the drawings, first, Figure 2 is a change in the residual magnetic flux density according to the change of the applied magnetic field during injection (A / B / C / D = 40/15/10 / 35, the injection temperature is 240 ° C, where the symbol-■-indicates the parallel direction of the applied magnetic field,-●-indicates the vertical direction of the applied magnetic field, and as can be seen from this figure, the magnetic field strength gradually starts to increase at 2 kOe. It is shown that the maximum residual magnetic flux density in the direction of applied magnetic field is 4 to 8 kOe, which is the most desirable surface magnetic flux density when the magnetic field strength is 4 to 8 kOe when the mixed pellet of binder and magnetic powder is injected in the magnetic field. It can be said that is obtained.

3 is a view showing the change in the powder anisotropy rate according to the magnetic field change during injection in the magnetic powder (strontium-ferrite) content of 87wt.%. Show the harmonies. 4 is a view showing the change in the powder anisotropy according to the change of the applied magnetic field at the injection of the magnetic powder content 82wt.%, The injection temperature is 240 ℃, the maximum anisotropy at the magnetic field strength 4 kOe ~ 8 kOe.

The present invention is explained more clearly through the following various examples, but is not intended to limit the present invention to such an embodiment.

Example 1

Inorganic powder is an anisotropic strontium ferrite (SrO-6Fe2O3) magnetic powder, which is a kind of ceramic powder, and has an average particle size of 0.8 to 1.2 µm. When the total content of the composition is 100 wt.%, The binder is 15 wt.% And the magnetic powder is 85 wt. % Was used. Prior to mixing this powder with the binder, the surface of the powder was coated with a silane coupling agent. The binder was composed of 40 wt.% Polypropylene, 10 wt.% Ethylene propylene, 40 wt.% Ethylene vinyl acetate, and 10 wt.% High density polyethylene when the total binder content was 100 wt.%. The magnetic powder and the organic binder were mixed in a mixer at 170 ° C. for 2 hours to make pellets. Samples made of pellets were injected in the form of an 8-pole anisotropic magnet roll for a laser printer in a magnetic field injection machine. The magnetic field intensity was 4 kOe at the time of injection, the temperature of the injection molded product was 240 ° C, and the temperature of the mold was 60 ° C. The surface magnetic flux density of the prepared magnetic roller was 750 ± 50G on the sleeve.

Example 2

Inorganic powder was an anisotropic samarium-cobalt (Sm2 (Co, Fe, M) 17 (2:17)) magnetic powder, which is a kind of rare earth-based alloy, and used as an average particle size of 3-5 μm, and the total content of the composition was 100 wt. In the case of%, 15 wt.% Of the binder and 85 wt.% Of the magnetic powder were used. The surface of the powder was coated with a coupling agent before the powder was mixed with the binder. The binder was composed of 45 wt.% Polypropylene, 10 wt.% Ethylene propylene, 35 wt.% Ethylene vinyl acetate, and 10 wt.% High density polyethylene when the total binder content was 100 wt.%. The magnetic powder and the organic binder were mixed in a mixer at a temperature of 170 ° C. for 2 hours to make pellets. The sample made of the wetlets was injected from a magnetic field injection machine in the form of an 8-pole anisotropic ring for a small DC motor. The magnetic field intensity at the time of injection was 7 kOe, the temperature of the injection product was 240 ° C, and the temperature of the mold was 60 ° C. The maximum magnetic energy of the prepared ring magnet was 10 MGOe. At this time, the residual magnet density was 6.7 kG and the coercive force was 5.2 kOe.

Example 3

As the inorganic powder, an anisotropic neodymium-iron-boron (Nd-Fe-B) magnetic powder, which is a kind of rare earth-based alloy, was used having an average particle size of 3-5 μm. When the total content of the composition was 100 wt.%, The binder was 11 wt. % And the magnetic powder was used to 89wt.%. The surface of the powder was coated using a coupling agent before the powder was mixed with the binder. The binder was composed of 40 wt% polypropylene, 10 wt% ethylene propylene, 35 wt% ethylene vinyl acetate, and 15 wt% high density polyethylene when the total content of the binder was 100 wt%. The magnetic powder and the organic binder were mixed in a mixer at 170 ° C. for 2 hours to make pellets. The pelletized sample was injected from a magnetic field injection machine in the form of an 8-pole anisotropic ring for small DC motors used in hard disk drives. The strength of the magnetic field at the time of injection was 8 kOe, the temperature of the injection molded product was 240 ° C, and the temperature of the mold was 60 ° C. The maximum magnetic energy of the prepared resin bond magnet was 17 MGOe, the residual magnetic flux density was 8.9 kG, and the coercive force was 12 kOe.

The present invention is a disadvantage in that high magnetic anisotropy is achieved by changing the magnetic field strength of the magnetic field injection machine using magnetic powder to produce anisotropic resin bond magnets having a uniform surface magnetic flux density, that is, a limitation in increasing the magnetic field strength. Phenomena such as the presence of and the nonuniform magnetic flux density of the molded body due to the nonuniform magnetic field strength have been improved by using a binder based on polypropylene having a high melt index.

In addition, by using a binder prepared by adding an ethylene propylene copolymer, an ethylene vinyl acetate copolymer, and a high density polyethylene to a polypropylene and a composition in which magnetic powders are mixed, molding in the preparation of anisotropic multipolar resin bond magnets by molding in the seed magnetic field There is no deterioration of magnetic properties due to deformation by post-shrinkage and movement of magnetic poles due to deformation, and excellent machinability during post-processing by lathe, so there is no deformation of molded body, etc. It is possible to manufacture a highly functional resin bond magnet that requires low physical properties and low water removal and requires precise magnetic properties and dimensional accuracy.

In addition, ethylene propylene, ethylene vinyl acetate and high density polyethylene are mixed with a polypropylene binder and magnetic powder to make pellets, and then injected at a magnetic field strength of 2 to 10 kOe according to the characteristics of the magnetic powder to have a uniform surface magnetic flux density. Resin-bonded magnets could be manufactured, and the cost of resin-bonded magnets could be reduced by using resins that are less expensive than nylon or rubber, which is a conventional binder.

In fact, when the resin bond magnet was prepared by injection molding by mixing 87 wt.% Of ferrite magnetic powder with 13 wt.% Of the polymer binder according to the present invention, the shrinkage of the molded product was 0.4%, the orientation of the magnetic powder was 89%, and the thermostat was heated at 50 ° C. The water absorption at was 0.092 wt.% (1.362 wt.% When nylon was used as the binder). In multipolar anisotropic resin bond magnets requiring precise magnetic properties and dimension accuracy, such as magnet rollers for LBP, the surface flux density falls within the error range due to the high flowability of the binder according to the present invention, and the longitudinal direction during post-processing by lathe machining It was possible to manufacture a product without modification to.

Claims (9)

A binder for producing a resin bond magnet comprising 30 to 95 wt.% Polypropylene, 5 to 20 wt.% Ethylene propylene, 5 to 20 wt.% High density polyethylene and 10 to 40 wt.% Ethylene vinyl acetate. 10-20 wt.% Of a binder consisting of 30 to 95 wt.% Polypropylene, 5 to 20 wt.% Ethylene propylene, 5 to 20 wt.% High density polyethylene and 10 to 40 wt.% Ethylene vinyl acetate when the total content of the composition is 100 wt.%. A composition for producing a resin bond magnet, comprising% and magnetic powder of 80 to 90 wt.%. The composition of claim 2, wherein the binder is 40 wt.% Polypropylene, 15 wt.% Ethylene propylene, 10 wt.% High density polyethylene and 35 wt.% Ethylene vinyl acetate. The composition for preparing a resin bond magnet according to claim 2, wherein the binder comprises 9 to 30 wt.% Of the binder and 70 to 90 wt.% Of the magnetic powder. When the total content of the composition is 100 wt.%, A binder consisting of 30 to 95 wt.% Polypropylene, 5 to 20 wt% ethylene propylene, 5 to 20 wt.% High density polyethylene and 10 to 40 wt.% Ethylene vinyl acetate is added. And a resin bond magnet production method comprising injection molding the composition for preparing a resin bond magnet comprising 80 wt% to 90 wt% of the magnetic powder in a pellet form at a magnetic field strength of 2 to 10 kOe in a temperature range of 170 ° C. to 250 ° C. in a magnetic field. . The method of claim 5, wherein the magnetic powder has a resin bond magnet manufacturing method having an average particle size of 0.8 ~ 5㎛. The magnetic powder according to claim 5, wherein the magnetic powder is anisotropic strontium ferrite (SrO-6Fe2O3) magnetic powder, anisotropic samarium-cobalt-based (Sm2 (Co, Fe, M) 17 (2:17)) magnetic powder and anisotropic neodymium-iron A resin bond magnet production method selected from the group consisting of boron (Nd-Fe-B) magnetic powder. 6. The method of claim 5, wherein the magnetic powder is surface coated with a silane coupling agent. The method of claim 8, wherein the surface coating is 50 to 80 ℃ temperature while injecting a mixture of ethyl alcohol and silane coupling agent corresponding to 0.1 to 1.0wt.% Of the magnetic powder in a weight ratio of 3: 1 to the magnetic powder The resin bond magnet manufacturing method which mixes in the mixer of Claim 1, and makes it dry in the oven of 80-100 degreeC temperature.