JP3191021B2 - Magnetic paint, magnetic layer for encoder and method for forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, in order to perform position control and speed control of a motor such as a motor, a magnetic encoder, for example, is used to accurately detect the number of rotations and the rotation angle of the motor. FIG. 6 is a perspective view showing a general magnetic encoder provided in the electric motor. As shown in the drawing, a drum base 6 as a base is fixed to a rotating shaft 4 of an electric motor 2 so that the drum base 6 can be integrally rotated. A magnetic layer having a thickness T1 of, for example, about 80 μm over the entire surface of the drum base 6 is provided. 8
And an N / S pole is formed on this surface with a magnetization pitch λ, for example, 125 μm. In the vicinity of the surface of the drum base 6, for example, 80 to 100 μm
The magnetic resistance element 10 is provided with a spacing X1 of m and detects a change in the magnetic field from the N and S poles due to the rotation of the drum base 6. It is configured to control the rotation and the rotation angle of the camera.

In order to form the magnetic layer 8 described above, for example, a magnetic powder made of Co-γFe ₂ O ₃ is formed by dispersing a polyvinyl butyral (PVB) resin as a dispersant, an epoxy resin and a phenol resin as a binder agent. In addition, a volatile magnetic solvent such as cellosolve acetate is mixed to form a liquid magnetic paint, and this magnetic paint is applied on the surface of the drum base 6 in two coats, for example, in a thickness of 1000 μm.
A layer of magnetic paint of about m is formed. Then, this layer is dried to evaporate a volatile solvent to a thickness of about 170 μm, and is polished precisely after drying and baking to finally form a magnetic layer 6 having a thickness of about 80 μm. The reason for this polishing is that, for example, if a foreign matter is contained in the coating film surface, the detection signal is affected, and the surface state is directly reflected in the surface magnetic field.

[0004] In this case, in the case of a contact-type detection head such as a normal magnetic tape, a magnetic field having a desired strength can be easily obtained on the surface of the magnetic layer.
Although it may be as thin as about μm, in this type of encoder, since it is a non-contact type detection system provided with the spacing L1, an appropriate magnetic field intensity on the surface of the magnetic layer is required to obtain an appropriate magnetic field intensity. The thickness of the magnetic layer is required. FIG.
FIG. 11 shows the calculation results of the relationship between the magnetic field strength on the magnetic layer surface and the magnetic layer thickness. Accordingly, when the ratio X / λ between the spacing X and the magnetization pitch λ is constant, the ratio d / λ between the thickness d of the magnetic layer and the magnetization pitch λ is as follows: It can be seen that the surface magnetic field intensity 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
μm or more is required. The inventor sets d at 80 μm in consideration of the processing allowance and the characteristic variation allowance.

[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 the coarse particles 18 contained in 4 are extruded near the surface by the reflux action of the paint accompanying the evaporation of the volatile solvent and are discharged. However, in order to effectively perform the reflux action, the viscosity of the paint is preferable. Is preferably about 7 to 8.5 poise (shear speed is 38.30 sec ^-1 ). The reason is that if the viscosity is higher than this, the reflux action is not performed sufficiently and bubbles and the like which cause defects are present in the paint. This is because the magnetic paint may remain, or cracks may be generated due to the bubbles, and if the viscosity of the paint is too small, the applied magnetic paint may drop from the drum base 6.

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

[0007] However, if the coating is performed twice as described above, not only is there a problem that much time is required for forming the magnetic layer, but also the chance of adhesion of dust and the like at the time of drying increases. There is a problem that defects easily occur. In this case, it is conceivable to simply increase the ratio of the solid component in order to thicken the coating film after drying, but if the ratio of the solid component is simply increased, the viscosity increases accordingly,
For this reason, there is a problem that air bubbles and the like contained in the coating film cannot be sufficiently discharged. The present invention has been devised in view of the above problems and effectively solving them. An object of the present invention is to provide a magnetic paint capable of forming a magnetic film having a desired thickness by a single application and a method for forming a magnetic layer for an encoder.

[0008]

SUMMARY OF THE INVENTION 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. It is made by obtaining the knowledge that the ratio of the solid component can be increased while increasing. According to a first aspect of the present invention, there is provided a magnetic recording medium having a magnetic layer formed on a curved surface such as a drum base.
A magnetic paint having a predetermined value of viscosity obtained by mixing a magnetic powder, a resin and a volatile solvent, wherein the viscosity of the magnetic paint is set within a range of 6.5 to 10.0 poise.
And the ratio of the volatile solvent to the solid component comprising the magnetic powder and the resin is set to 1.70 or less . According to a second aspect of the invention, a magnetic layer for an encoder is obtained by applying the magnetic paint obtained in the first aspect of the present invention on a substrate.

[0009]

The first aspect of the present invention is to use a resin having a relatively low viscosity and a small degree of polymerization and a small number of repeating units as a resin, thereby maintaining the viscosity at the same value as that of the conventional coating and reducing the ratio of the solid component in the coating. It can be set much larger than in the case of the conventional paint. A second invention provides a method of applying the magnetic paint obtained in the first invention on a substrate,
Since the ratio of the solid component is high, a magnetic layer having a desired thickness can be obtained by one application.

[0010]

EXAMPLES Hereinafter, be described in detail with reference magnetic paint according to the present invention, an example of a method of forming a magnetic layer and child for the encoder to the accompanying drawings. First, in order to confirm the appropriate viscosity of the magnetic paint, the ease of application of the paint, the occurrence of cracks, and the occurrence of pores were examined when the viscosity was variously changed. The results are shown in Table 1 below.

[0011]

[Table 1]

As is apparent from Table 1, if the paint viscosity is smaller than 6.5 poise, the paint dripping occurs. If the viscosity exceeds 10 poise, the spread of the paint becomes poor and it becomes difficult to apply. And it turns out that the ease of application is the best when the viscosity is 8.2 poise. When the viscosity of the coating material becomes 15.0 poise, cracks and pores are generated together. Therefore, it is found that the viscosity of the magnetic coating material is preferably in the range of 6.5 to 10.0 poise.

Next, a method for producing a magnetic paint and a method for forming a magnetic layer for an encoder will be described. FIG. 1 is a flowchart showing a schematic method for forming a magnetic paint and a magnetic layer, FIG. 2 is a flowchart showing a method for producing a magnetic paint, and FIG. 3 is a diagram for explaining a method for applying a magnetic paint to a drum substrate. FIG. First, as shown in FIG. 1, in S1, a magnetic powder, a PVB resin as a binder resin and a volatile component are charged into a kneader having a plurality of blades, and these are kneaded. When the kneading is completed, the epicoat resin or phenol resin is added in S2, and the mixture is stirred in a ball mill containing stainless steel balls having a diameter of several mm or a sand mill containing glass beads or the like, and dispersed. Perform the treatment to complete the magnetic paint.

[0014] be described with reference to a flow showing the manufacturing process of the magnetic paint 2 specifically, first, as the magnetic powder, for example, a predetermined amount of Co-γFe ₂ O _3, for example 70
0.2 g is weighed, and as a PVB resin, for example, Sekisui Chemical's ELEX B (trademark) low polymerization degree type BL-1, BL-
2. A predetermined amount, for example, 70.6 g of any of BL-3, BL-S, and BX-L, for example, BX-L, is weighed (S21). As a conventional magnetic paint, the viscosity is 70-
A high polymerization degree type as high as 140 poise, for example, BX-1, was used. In the present invention, a low polymerization degree type resin is used as described above. The viscosity of the low-polymerization type resin is in the range of 10 to 60 poise, and the viscosity of the low-polymerization type BX-L is a very small value of 10 to 30 poise. The structural formula of Elex B is represented by the following chemical formula 1.

[0015]

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The thermal / mechanical properties and viscosity of the resin depend on the degree of polymerization of the structural formula. In the present invention, a resin having a low degree of polymerization is used. When the weighing is completed in this way, these are charged into a kneader having a plurality of blades, and a predetermined amount of a volatile solvent, for example, cellosolve acetate represented by the following formula, for example, 150.4 g is added. (S22), kneading is performed. According to the kneading operation of CH ₃ COOCH ₂ CH ₂ OC ₂ H ₅ , cellosolve acetate, for example, 135.4 g and 275.2 g are sequentially added (S23, S24). When the kneading operation for a predetermined time is completed in this way, 288.8 g of butyl cellosolve represented by the following chemical formula, for example, is added as another volatile component to the kneader mixture, for example, 900.6 g, and a solvent is prepared ( (S25) Then, premixing is performed for a predetermined time (S26).

After the premixing is completed, 173.0 g of an epoxy resin and 103.8 g of a phenol resin are added as solid components to prepare a resin (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 is used.
1, 1002, 1003, 1055, 1004, 100
Any type of 4AF, for example, grade 100
Use 1. The molecular weight of a conventional magnetic paint is about 290.
Although grade 1007 which is 0 and has a large viscosity was used, in this embodiment, as described above, a phenol resin having a small molecular weight and a low viscosity was used,
In particular, the molecular weight of the above grade 1001 is as very small as about 900. The structural formula of this epicoat is represented as shown in the following chemical formula 2.

[0018]

Embedded image

The smaller the repeating unit n in this structural formula is,
An epicoat having a small repeating unit n is selected as described above because of its low molecular weight. As the phenol resin, the same material as that used for the conventional magnetic paint, for example, Methylon 75108 (trademark) as shown in Chemical Formula 3
Is used.

[0020]

Embedded image

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

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

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 anodized aluminum surface is subjected to alumite treatment to complete the drum substrate (S
3) Then, the surface of the drum base 6 is ultrasonically cleaned (S4). When the cleaning of the drum base 6 is completed in this way, the magnetic paint prepared previously is applied to the surface of the drum base 6 using the coating apparatus shown in FIG. 3 (S5). More specifically, this magnetic paint application device accommodates a paint bottle 20 filled with a magnetic paint 14 in a pressurized tank 22, and provides the magnetic paint 14 that has been pressure-fed in a pipe 24 by this pressure in the middle of the pipe. Nozzle 26 of valve 28 with nozzle
The magnetic paint 14 is applied to the surface of the drum base 6 which is rotating. The magnetic paint 14 flowing through the pipe 24 at this time
Is controlled by a dispenser controller 30, and the on / off of the device is controlled by a foot switch 32 connected to the controller 30.

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

As described above, by using a resin having a low viscosity as a simple resin and a small degree of polymerization and a small number of repeating units as a binder resin, which is a material of the magnetic paint, the conventional paint can be used without changing the viscosity as the magnetic paint. The ratio of the solid component can be increased by about 1.67 times as compared with. Therefore, even if applied with the same coating thickness as that of the conventional paint, a coating film having a thickness of about 1.67 times can be obtained after drying.
In order to obtain a coating film having a thickness equivalent to that of the dried coating film for 00 μm (two-layer coating of 400 μm + 600 μm), it is found that the magnetic paint of this embodiment only needs to be applied once with a thickness of about 600 μm.

Therefore, the desired thickness of the magnetic layer can be finally obtained by one application by using the magnetic paint according to the present embodiment. Since the process can be simplified, not only the manufacturing time can be shortened, but also the possibility that defects due to adhesion of dust and the like can be reduced due to the reduction in the number of processes. The viscosity of the magnetic paint is 6.5 to 10.0.
The range of poise is preferable, and the viscosity is particularly preferably about 8.5. The ratio of the volatile solvent to the solid component, that is, the ratio of the volatile component / solid component is set to 1.70 or less.

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

[0028]

[Table 2]

In both Example 1 and Comparative Example 1, Co-γFe203 was used as a magnetic powder, cellosolve acetate and butyl cellosolve were used as volatile components, and a phenol resin (Methylon 75108) was used as a part of the resin.
Was used. And as a PVB resin as a dispersant of Comparative Example 1, a high polymerization degree type having a large viscosity (BX-1)
Epoxy coat 1007 having a large repeating unit n and a large molecular weight and high viscosity was used as an epoxy resin as a binder agent. On the other hand, as the PVB resin as a dispersant of Example 1, a resin of a low polymerization degree type (BX-L) having a small viscosity is used, and as an epoxy resin as a binder agent, the repeating unit n is small and the molecular weight and Epicoat 100 with low viscosity
1 was used. In this case, the filling rates of the magnetic powders 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, ball milling, and the like in the same manner as described in the previous examples to produce magnetic coatings, and the respective coatings were applied to a drum substrate. As is clear from Table 2, the ratio of the solid component representing the coating film volume (thickness) after the coating and drying treatments is as follows:
In contrast to the conventional paint, which is 17.38% by volume, the magnetic paint of Example 1 is 28.95% by volume. As a result, even when the paints of Example 1 and Comparative Example 1 are applied with the same thickness, the thickness of the coating film after drying is about 1.67 times thicker in Example 1 than in Comparative Example 1. It can be assumed that it is formed. FIG. 4 is a graph showing the relationship between the thickness at the time of application of the magnetic paints of Example 1 and Comparative Example 1 and the film thickness after drying measured by a high-frequency film thickness meter.

According to this graph, for example, when a two-layer coating is performed in Comparative Example 1 and the total coating thickness is set to 1000 μm, a film thickness of about 160 μm is obtained after drying. It was found that the coating thickness of Comparative Example 1 for obtaining the composition was about 600 μm, and that the coating thickness of Example 1 could be about 0.6 times the coating thickness. Table 3 shows that volatile components and solid components (magnetic powder + PVB resin + epoxy resin + phenol) were obtained by using exactly the same materials as those used in Example 1 as Example 2 and appropriately changing the amounts of the respective materials. (Resin) and four types of magnetic paints were produced, and their viscosities corresponded to the materials. FIG. 5 is a graph showing the relationship between the value of the ratio between the volatile component and the solid component in Table 3 and the viscosity. The viscosity was measured using an E-type viscometer.

[0032]

[Table 3]

According to this graph, all the four types of magnetic paints have good stickiness and a good viscosity of 6.5 to 10 poise, and in order to make the magnetic paint have a viscosity of 6.5 or more, it is volatile. It turns out that the ratio of the component to the solid component should be set to 1.70 or less. Further, a coating film having a thickness of about 600 μm was formed on the surface of the drum substrate in a single application using the four types of magnetic coating materials manufactured according to the amounts shown in Table 3, and dried. About 160μ at
It has been found that a desired thickness of about m can be obtained. In the above examples, a low polymerization type of ELEX was used as the PVB resin, and an epicoat having a small repeating unit was used as the epoxy resin.
The resin is not limited to the above resins as long as the resin has a low viscosity and a small degree of polymerization and a small repeating unit.

[0034]

As described above, according to the present invention, the following excellent functions and effects can be exhibited. Since a resin having a small degree of polymerization and a small number of repeating units is used, a magnetic coating material having a large ratio of solid components can be obtained while maintaining easy-to-coat viscosity. Therefore, by using the above-mentioned magnetic paint, the curved surface of the drum base or the like is caused by air bubbles.
By applying the magnetic paint in a single application without causing cracks or dripping of the magnetic paint, drying and polishing it
Thus, a magnetic layer having a desired thickness can be obtained.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a flow of a 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 paint.

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 a relationship between a coating thickness and a film thickness of a magnetic paint of the present invention and a conventional paint.

FIG. 5 is a graph showing the relationship between the volatile component / solid component and the viscosity of the magnetic paint 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 released from a magnetic paint applied on a drum base.

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

[Explanation of symbols]

 Reference Signs List 2 motor 4 rotating shaft 6 drum base (base) 8 magnetic layer 10 magnetoresistive element 12 servo circuit T1 film thickness X1 spacing λ1 magnetization pitch

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C09D 5/23

Claims (4)

(57) [Claims] A magnetic layer is formed on a curved surface of a drum base or the like.
In a magnetic paint, a magnetic paint having a viscosity of a predetermined value obtained by mixing a magnetic powder, a resin and a volatile solvent,
The viscosity of the magnetic paint is in the range of 6.5 to 10.0 poise.
And a ratio of the volatile solvent to a solid component comprising the magnetic powder and the resin is set to 1.70 or less . 2. The method according to claim 1, wherein the magnetic paint is a drum.
By applying on a curved surface of a substrate, drying and polishing
Forming a magnetic layer, and magnetizing the magnetic layer at a predetermined pitch;
For encoders characterized by being formed by
Magnetic layer. 3. The method according to claim 1, wherein the magnetic coating material has a thickness of 600 to 1000 μm.
m and dried to a film thickness of 160 to 270 μm.
m, and by polishing to remove defects,
The thickness of the layer should be set in the range of 80-130 μm.
3. The magnetic layer for an encoder according to claim 2, wherein: Upon 4. A dried magnetic coating material is applied onto a substrate to form a magnetic layer of the encoder, the magnetic coating, the encoder characterized in that said a magnetic coating according to claim 1 Of forming a magnetic layer for use.