JPH0616976A - Magnetic coating and method for forming magnetic layer for encoder - Google Patents

Abstract

PURPOSE:To provide a magnetic coating having high solid ratio while keeping the suitable viscosity for coating, useful for forming a magnetic layer for an encoder of magnetic drum, etc., and capable of forming a magnetic layer having desired thickness by single coating process. CONSTITUTION:The magnetic coating is produced by mixing (A) magnetic powder (e.g. Co-gamma Fe2O3) with (B) a resin (e.g. polyvinyl butyral resin) and (C) a volatile solvent (e.g. Cellosolve acetate). The ratio of the component C to the solid component consisting of the components A and B is set to a low level while keeping the viscosity of the coating to a prescribed level. Preferably, the viscosity of the coating is 8.5 poise and the ratio of the component C to the solid component is set to <=1.7. A soft resin having low viscosity is preferably used as the component B to decrease the ratio of the component C to the solid component while keeping the viscosity of the magnetic coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in a magnetic coating material for forming a magnetic layer for an encoder such as a magnetic drum and a method for forming the magnetic layer.

[0002]

2. Description of the Related Art Generally, in order to perform position control and speed control of an electric motor such as a motor, a magnetic encoder, for example, is used in order to accurately detect the rotational speed and rotational angle of the electric motor. FIG. 6 is a perspective view showing a general magnetic encoder provided in an electric motor. As shown in the figure, a drum base 6 as a base is fixed to the rotary shaft 4 of the electric motor 2 so as to be integrally rotatable, and a magnetic layer having a thickness T1 of, for example, about 80 μm over the entire surface of the drum base 6. 8
And the N and S poles are formed on this surface with a magnetizing pitch λ, for example, 125 μm. Then, in the vicinity of the surface of the drum base 6, for example, 80 to 100 μm
A magnetic resistance element 10 is provided with a spacing X1 of m between them to detect a change in the magnetic field from the N / S poles due to the rotation of the drum base 6, and the detection result is sent to the servo circuit 12 to output the electric motor 2 It is configured so that the rotation and the rotation angle of the can be controlled.

In order to form the above-mentioned magnetic layer 8, for example, a polyvinyl butyral (PVB) resin as a dispersant, an epoxy resin and a phenol resin as a binder are added to a magnetic powder of Co-γFe ₂ O ₃ . In addition to this, a volatile solvent such as cellosolve acetate is mixed to form a liquid magnetic paint, and this magnetic paint is applied to the surface of the drum substrate 6 twice in a divided manner, for example, to obtain a thickness of 1000 μm.
A layer of magnetic paint of about m is formed. Then, this layer is dried to evaporate the volatile solvent to have a thickness of about 170 μm, and is further precisely baked after dry baking to finally form the magnetic layer 6 having a thickness of about 80 μm. The reason for polishing in this way is that, for example, if the coating film surface contains a foreign substance, the detection signal is affected, and the surface state is directly reflected in the surface magnetic field.

In this case, in the case of a contact type detection head such as an ordinary magnetic tape, a desired magnetic field strength can be easily obtained on the surface of the magnetic layer, so that the thickness of the magnetic layer is 2.5.
Although it can be as thin as about μm, this type of encoder is a non-contact type detection system provided with a spacing L1 and therefore is suitable for obtaining a desired magnetic field strength on the surface of the magnetic layer. The thickness of the magnetic layer is required. Figure 8
The calculation results of the relationship between the magnetic field strength on the surface of the magnetic layer and the thickness of the magnetic layer are shown in. From this, when the ratio X / λ of the spacing X and the magnetic pitch λ is constant, the ratio d / λ of the thickness d of the magnetic layer to the magnetic pitch λ is as follows: It can be seen that the surface magnetic field strength becomes weak. For example, X / d = 0.
To obtain a surface magnetic field of 50 Gauss at 75, d / λ> 0.4
6 is required. When λ = 125 μm, d is 57
At least μm is required. The present inventor considers the processing allowance and the characteristic variation allowance and sets d to 80 μm.

[0005]

Immediately after the magnetic paint is applied to the drum base 6, the magnetic paint 1 applied to the surface of the drum base 6 as shown in FIG.
The bubbles 16 and coarse particles 18 contained in 4 are extruded to the vicinity of the surface by the reflux action of the coating material due to the evaporation of the volatile solvent and discharged. However, the viscosity of the coating material is preferable in order to effectively carry out this refluxing action. Is about 7 to 8.5 poise (slipping speed is 38.30 sec ⁻¹ ) because the viscosity is higher than this, the reflux action is not sufficiently performed, and bubbles or the like that cause defects in the paint. The reason for this is that the magnetic coating material remains or cracks are generated due to the bubbles, and conversely, if the viscosity of the coating material is too small, the applied magnetic coating material drops from the drum base 6.

As the epoxy resin or PVB resin which is the raw material of the above magnetic paint, a resin having a considerably large viscosity and a large molecular weight is used, and the ratio of the solid components constituting the magnetic powder and the various resins is about 17.38 Vol%. And the final thickness of the magnetic layer after polishing is set to 80 to 1 as described above.
In order to set the thickness to 30 μm, it was applied twice so as to have a thickness of 400 μm + 600 μm. The thickness of the coating material that can be formed by one coating operation is about 600 μm at maximum, and if the coating material is thicker than that, the above-mentioned bubbles may not be discharged sufficiently.

However, in addition to the problem that it takes a lot of time to form the magnetic layer when the coating is performed twice, the chances of dust adhesion during drying increase and the defect is caused. There is a problem that defects are likely to occur. In this case, it is possible to simply increase the ratio of the solid component in order to increase the thickness of the coating film after drying, but if the ratio of the solid component is simply increased, the viscosity increases accordingly,
Therefore, there is a problem that bubbles and the like contained in the coating film cannot be sufficiently discharged. The present invention has been made to pay attention to the above problems and to solve them effectively. An object of the present invention is to provide a magnetic paint capable of forming a magnetic film having a desired thickness with one coating and a method for forming a magnetic layer for an encoder.

[0008]

The present invention maintains the viscosity of a magnetic paint in the same manner as before by using a softer resin having a lower viscosity as an epoxy resin or a PVB resin used as a magnetic paint. However, it was made by obtaining the knowledge that the ratio of solid components can be increased. In order to solve the above-mentioned problems, a first invention is a magnetic paint having a predetermined value of viscosity, which is obtained by mixing magnetic powder, a resin and a volatile solvent, and the viscosity of the magnetic paint is set to a predetermined value. While maintaining the ratio, the ratio of the volatile solvent to the solid component composed of the magnetic powder and the resin is set small. A second invention is configured to obtain a magnetic layer for an encoder by applying the magnetic coating material obtained in the first invention on a substrate.

[0009]

According to the first aspect of the invention, for example, by using a resin having a relatively low viscosity and a small degree of polymerization or a repeating unit as a resin, the ratio of the solid components in the coating material can be maintained while maintaining the viscosity at the same value as that of the conventional coating material. It is possible to set a considerably larger value than in the case of the conventional paint. The second invention is such that when the magnetic coating material obtained in the first invention is applied onto a substrate,
Since the ratio of the solid component is high, it is possible to obtain a magnetic layer having a desired thickness by one application.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnetic coating material and a method of forming a magnetic layer for an encoder according to the present invention will be described in detail below with reference to the accompanying drawings. First, in order to confirm the appropriate viscosity of the magnetic paint, the ease of applying the paint when various viscosities were changed, the presence or absence of cracks, and the presence or absence of pores were examined. The results are shown in Table 1 below.

[0011]

[Table 1]

As is clear from Table 1, when the viscosity of the coating is less than 6.5 poise, dripping of the coating occurs, and when the viscosity exceeds 10 poise, the spread of the coating becomes poor and it becomes difficult to apply. Then, it was found that the ease of application was the best when the viscosity was 8.2 poise. Further, when the paint viscosity becomes 15.0 poise, both cracks and pores are generated. Therefore, it is found that the viscosity of the magnetic paint is in the range of 6.5 to 10.0 poise.

Next, a method of manufacturing the magnetic paint and a method of forming the magnetic layer for the encoder will be described. FIG. 1 is a flow showing a schematic method for forming a magnetic coating material and a magnetic layer, FIG. 2 is a flow showing a method for manufacturing a magnetic coating material, and FIG. 3 is a flow chart showing a method for applying a magnetic coating material to a drum substrate. FIG. First, as shown in FIG. 1, in S1, magnetic powder, PVB resin as a binder resin, and volatile components are charged into a kneader having a plurality of blades and kneaded. After this kneading is completed, in S2, epicoat resin, phenol resin, etc. are added, and the mixture is stirred in a ball mill containing stainless balls having a diameter of several mm or in a sand mill containing glass beads to disperse. Processing is performed to complete the magnetic paint.

The manufacturing process of this magnetic coating material will be described in detail with reference to the flow chart shown in FIG. 2. First, as the magnetic powder, for example, Co-γFe ₂ O ₃ in a predetermined amount, for example, 70
0.2 g is weighed and used as a PVB resin, for example, Sekisui Chemical's Elex B (trademark) low polymerization degree type BL-1, BL-.
2, BL-3, BL-S, or BX-L, for example, BX-L is weighed in a predetermined amount, for example, 70.6 g (S21). The conventional magnetic paint has a viscosity of 70-
A high polymerization type of 140 poise, for example, BX-1 was used, but in the present invention, a low polymerization type resin is used as described above. The low-polymerization type resin has a viscosity in the range of 10 to 60 poise, and particularly the low-polymerization type BX-L has a very small value of 10 to 30 poise. The structural formula of this Elex B is represented as shown in Chemical Formula 1 below.

[0015]

[Chemical 1]

The thermal and mechanical properties and viscosity of the resin depend on the degree of polymerization of this structural formula, and a resin having a low degree of polymerization is used in the present invention. When the weighing is completed in this way, these are put into a kneader machine having a plurality of blades, and a predetermined amount, for example, 150.4 g of cellosolve acetate represented by the following rational formula is added as a volatile solvent. (S22), kneading is performed. As the CH ₃ COOCH ₂ CH ₂ OC ₂ H ₅ kneading operation is performed, 135.4 g and 275.2 g of cellosolve acetate are sequentially added, respectively (S23, S24). When the kneader kneading operation for a predetermined time is completed in this manner, for example, 908.8 g of this kneader mixture is mixed with another volatile component such as 288.8 g of butyl cellosolve represented by the following formula to prepare a solvent ( After that, premixing is performed for a predetermined time (S26).

When the premixing is completed in this way, a resin is prepared by adding, for example, 173.0 g of an epoxy resin and 103.8 g of a phenol resin as solid components (S27). In this case, as the epoxy resin, for example, Grade 100 having a relatively low molecular weight and a relatively low viscosity in Epicoat (trademark) of an oiled shell
1, 1002, 1003, 1055, 1004, 100
Any type of 4AF, eg Grade 100
1 is used. The conventional magnetic paint has a molecular weight of about 290
Although grade 1007 having a viscosity of 0 and a large viscosity was used, in this example, a phenol resin having a small molecular weight and a low viscosity was used as described above.
Particularly, the molecular weight of the above grade 1001 is very small, about 900. The structural formula of this epicoat is represented by the following chemical formula 2.

[0018]

[Chemical 2]

The smaller the repeating unit n in this structural formula,
Due to the low molecular weight, epicoats with low repeat units n are selected as described above. As the phenol resin, a material similar to that used for a conventional magnetic coating material, for example, Methylon 75108 (trademark) as shown in Chemical Formula 3 is used.
To use.

[0020]

[Chemical 3]

When the mixing of the resin is completed in this way, as described above, the mixture of these is placed in a ball mill containing a large number of stainless balls having a diameter of several mm or a sand mill containing glass beads and the like. The dispersion process is performed by stirring for a predetermined time (S28). By this agitation, the particles of the mixture are caught between the balls and subjected to impact force and strong shear stress, and the dispersion effect is exhibited. This completes the production of the magnetic paint. The ratio of the volatile solvent (cellosolve acetate, butylcellosolve) to the solid component (magnetic powder, various resins) of this magnetic paint, that is, the volatile component / solid component is about 2.37.

As described above, in this embodiment, each resin used in comparison with the conventional paint has a low viscosity and is soft, and a volatile solvent (cellosolve acetate, It is configured so that the amount of butyl cellosolve used is suppressed and the ratio of solid components (magnetic powder, various resins) is increased while maintaining the same viscosity as that of conventional paints. In this case, the ratio of the solid component of the conventional paint is about 1
In contrast to 7.38 Vol%, the ratio of the solid component in this example is about 28.95 Vol%, which can be greatly improved. The filling rate of magnetic powder and the amount of magnetic powder are set to the same values as those of conventional paints.

Returning to the flow shown in FIG. 1, the drum base 6 (see FIG. 6) is processed in parallel with the production of the magnetic paint. Specifically, the surface of the annular aluminum is anodized to complete the drum substrate (S
3) After that, the surface of the drum substrate 6 is ultrasonically cleaned (S4). When the cleaning of the drum substrate 6 is completed in this way, the magnetic coating material produced previously is applied to the surface of the drum substrate 6 using the coating device shown in FIG. 3 (S5). Specifically, this magnetic paint coating device stores a paint bottle 20 filled with the magnetic paint 14 in a pressure tank 22, and the magnetic paint 14 pressure-fed in the pipe 24 by this pressing force is provided in the middle of the pipe. Nozzle 26 of valve 28 with nozzle
The magnetic paint 14 is applied to the surface of the rotating drum substrate 6. Magnetic paint 14 flowing in the pipe 24 at this time
Is controlled by the dispenser controller 30, and the device is turned on / off by a foot switch 32 connected to the controller 30.

At this time, the excess magnetic paint adhering to the surface of the drum base is scraped off by the squeegee 34 and applied once to a predetermined thickness, for example, about 600 μm.
Here, the thickness of the coating film of 600 μm in this example is
Conventional two-layer coating film thickness with a low ratio of solid components 1
It becomes equivalent to 000 μm (400 μm + 600 μm),
Therefore, in order to obtain the final thickness of the magnetic layer (after dry polishing), for example, 80 μm, by using the magnetic coating film according to the present embodiment, the coating layer having a thickness of about 600 μm may be applied once. It turns out. When the coating operation of the magnetic coating material is completed in this way, the magnetic coating film is dried at a predetermined temperature to remove the volatile components, and the thickness of about 170 μm.
A magnetic layer 8 of about m is obtained (S6). Then, the surface of the magnetic layer 8 after drying is subjected to a polishing treatment to remove the surface portion that is likely to contain defects, and finally the magnetic layer 8 having a desired thickness, for example, 80 μm is obtained (S7). Then, the obtained magnetic layer 8 is magnetized with N and S poles at a predetermined magnetizing pitch λ1 to complete the magnetic layer 8 for an encoder (S8).

Thus, by using a resin having a low viscosity as a simple substance resin and a small degree of polymerization or a small number of repeating units as the binder resin which is a material of the magnetic paint, the conventional paint can be used without changing the viscosity of the magnetic paint. It became possible to increase the ratio of solid components by about 1.67 times as compared with. Therefore, even if the same coating thickness as in the case of the conventional coating material is applied, a coating film having a thickness of about 1.67 times can be obtained after drying.
It is clear that in order to obtain a coating film having the same thickness as the coating film after being dried for 00 μm (two-layer coating 400 μm + 600 μm), the magnetic coating material of this example should be applied once with a thickness of about 600 μm.

Therefore, by using the magnetic coating material according to this embodiment, the desired thickness of the magnetic layer can be finally obtained by one coating, and the magnetic coating can be manufactured as compared with the case where the conventional coating is twice coated. Since the process can be simplified, not only the manufacturing time can be shortened, but also the number of processes can be reduced, which can reduce the possibility of defects due to adhesion of dust and the like. The viscosity of the magnetic paint is 6.5-10.0.
The range of poise is preferable, and the viscosity of about 8.5 is particularly preferable. Further, the ratio of the volatile solvent to the solid component, that is, the volatile component / solid component is set to 1.70 or less.

Next, the magnetic coating material of the present invention and the conventional magnetic coating material were formed with the compounding amounts shown in Table 2, and the thicknesses when magnetic coating films were formed using these are compared. First, the magnetic coating material of the present invention was prepared with the compounding amounts shown in Example 1 of Table 2 to form a magnetic coating film, and the conventional magnetic coating material is shown in Table 2.
Comparative Example 1 is compared with the thickness when the magnetic coating film is formed with the compounding amount shown in Comparative Example 1.

[0028]

[Table 2]

In both Example 1 and Comparative Example 1, Co-γFe203 was used as the magnetic powder, cellosolve acetate and butyl cellosolve were used as the volatile components, and a phenol resin (Methylon 75108) was used as a part of the resin.
Was used. And, as the PVB resin as the dispersant of Comparative Example 1, a high polymerization type (BX-1) having a large viscosity
As the epoxy resin as the binder agent, Epicoat 1007 having a large repeating unit n and a large molecular weight and a large viscosity was used. On the other hand, as the PVB resin as the dispersant of Example 1, a low polymerization type (BX-L) resin having a low viscosity was used, and as the epoxy resin as the binder agent, the repeating unit n was small and the molecular weight and Epicoat 100 with low viscosity
1 was used. In this case, the magnetic powder filling rates of Example 1 and Comparative Example 1 were both set to 65 wt%, and the viscosities were both set to 8.0 poise.

These materials were subjected to kneader kneading treatment, ball mill treatment and the like in the same manner as described in the previous examples to produce magnetic paints, and the respective paints were applied to the drum substrate. As is clear from Table 2, the ratio of the solid component representing the coating film volume (thickness) after the coating treatment and the drying treatment is
In the conventional paint, the amount is 17.38 Vol%, whereas in the magnetic paint of Example 1, the amount is 28.95 Vol%. As a result, even if the paints of Example 1 and Comparative Example 1 were applied at the same thickness, the thickness of the coating film after drying was about 1.67 times thicker in Comparative Example 1 than in Comparative Example 1. It can be presumed that it is formed. FIG. 4 is a graph showing the relationship between the thickness of the magnetic paint of Example 1 and Comparative Example 1 at the time of application and the film thickness after drying measured by a high frequency film thickness meter.

According to this graph, for example, when two layers are applied in Comparative Example 1 and the coating thickness is set to 1000 μm in total, a film thickness of about 160 μm is obtained after drying. The coating thickness of Comparative Example 1 for obtaining the above is about 600 μm, and it was found that the coating thickness of the coating of Example 1 was about 0.6 times. Further, Table 3 shows that volatile components and solid components (magnetic powder + PVB resin + epoxy resin + phenol) were prepared by using the same materials as those used in Example 1 as Example 2 and appropriately changing the compounding amount of each material. (4) Different types of magnetic paints were produced by changing the ratio with the resin, and the viscosities of these were made to correspond to the materials. FIG. 5 is a graph showing the relationship between the value of the ratio of the volatile component and the solid component in Table 3 and the viscosity. An E-type viscometer was used for this viscosity measurement.

[0032]

[Table 3]

According to this graph, all four types of magnetic paints are in a viscosity range of 6.5 to 10 poise with good stickiness, and moreover, volatilization is required to make the viscosity of the magnetic paint 6.5 or more. It turns out that the ratio of the components to the solid components should be set to 1.70 or less. In addition, a coating film having a thickness of about 600 μm was formed in a single coating on the surface of the drum substrate by using the four types of magnetic coating materials prepared in the blending amounts shown in Table 3 and dried. At about 160μ
It has been found that a desired film thickness of about m can be obtained. In the above examples, the low polymerization degree type of Elex was used as the PVB resin, and the epicoat having a small repeating unit was used as the epoxy resin.
The resin is not limited to the above resins as long as it has a low viscosity and a small degree of polymerization or a small repeating unit.

[0034]

As described above, according to the present invention, the following excellent operational effects can be exhibited. Since a resin having a small degree of polymerization and a small repeating unit is used, it is possible to obtain a magnetic coating material having a large proportion of solid components while maintaining a viscosity that is easy to apply. Therefore, by using the above-mentioned magnetic paint, it is possible to obtain a magnetic layer having a desired thickness with a single coating.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of a schematic method for forming a magnetic paint and a magnetic layer.

FIG. 2 is a diagram showing a flow of a method for producing a magnetic coating material.

FIG. 3 is an explanatory diagram for explaining a method of applying a magnetic paint to a drum base.

FIG. 4 is a graph showing the relationship between the coating thickness and film thickness of the magnetic paint of the present invention and the conventional paint.

FIG. 5 is a graph showing the relationship between the volatile component / solid component and the viscosity of the magnetic coating material of the present invention.

FIG. 6 is a configuration diagram showing a general magnetic rotary encoder.

FIG. 7 is an explanatory diagram for explaining a state in which bubbles and the like are discharged from the magnetic coating material applied on the drum substrate.

FIG. 8 is a diagram illustrating the surface magnetic field strength of a Co—γFe ₂ O ₃ magnetic coating film.

[Explanation of symbols] 2 electric motor 4 rotating shaft 6 drum base (base) 8 magnetic layer 10 magnetoresistive element 12 servo circuit T1 film thickness X1 spacing λ1 magnetizing pitch

Claims (4)

[Claims] 1. A magnetic paint comprising a mixture of magnetic powder, a resin and a volatile solvent and having a predetermined value of viscosity, wherein the magnetic powder and the resin are maintained while maintaining the viscosity of the magnetic paint at a predetermined value. A magnetic coating material, characterized in that the ratio of the volatile solvent to the solid component is made small. 2. The resin has a low viscosity and a low degree of polymerization and / or a repeating unit.
The magnetic paint described. 3. The viscosity of the predetermined value is 6.5 to 1
The magnetic paint according to claim 1 or 2, wherein the ratio of the volatile solvent to the solid component is set to 1.70 or less while being set within a range of 0.0 poise. 4. When the magnetic coating material is applied onto a substrate and dried to form a magnetic layer for an encoder, the magnetic coating material is the magnetic coating material according to any one of claims 1 to 3. Method for forming magnetic layer for encoder.