JPH02284966A - Production of magnetic coating - Google Patents

Abstract

PURPOSE:To obtain a magnetic coating capable of providing an uniform coating film having excellent characteristics to a magnetic recording medium by dispersing pulverized magnetic powder having large specific surface area into a resin at a specific ratio. CONSTITUTION:For example, (B) an epoxy resin is blended with (A) magnetic powder having >=38m<2>/g BET value (specific surface area) at a resin amount of >=0.004g based on 1m<2> total surface area of the component A and the blend is subjected to first kneading using a kneader, etc., in 10-400kg/cm<2> shearing stress. Then (C) as necessary a resin and (D) solvent are added thereto and the blend is subjected to second kneading in shearing stress smaller than the above-mentioned shearing stress to provide the aimed magnetic coating.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to a method for producing a magnetic coating material for forming a coating film on a magnetic recording medium used in a storage device or the like. [Prior Art] Conventionally, magnetic paints for forming coating films on magnetic recording media have been disclosed in Japanese Patent Application Laid-Open No. 56-44712 and Japanese Patent Publication No. 57-44.
As described in Japanese Patent Application No. 712, magnetic powder and a resin as a polymeric binder are mixed and kneaded with a large abrasion stress, and then a resin as a polymeric binder and a solvent are added to this mixture and mixed. They continued to knead and manufacture it. The above-mentioned first kneading is performed using, for example, a kneader in order to apply a large abrasion stress, and the magnetic powder is sufficiently dispersed in this step. Furthermore, in order to obtain a composition that exhibits excellent properties when formed into a coating film, a polymeric binder and a solvent are added to the mixture and kneaded. This second kneading is carried out using, for example, a ball mill, since there is no need to apply a large shear stress as in the case of the first kneading.

[Problem to be solved by the invention]

The above conventional technology has been miniaturized. Specific surface area (BET value)
Not enough consideration has been given to the use of magnetic paints that use magnetic powders with large magnetic particles, and when such magnetic powders are used, there is a problem in that the coating film properties of magnetic recording media are not sufficient. Ta. An object of the present invention is to provide a method for producing a magnetic paint using finely divided magnetic powder having a large specific surface area.

[Means for Solving the Problems] The above object is to first knead at least a magnetic powder and a resin with a large shear stress to form a kneaded product, and further add at least one kind of resin that is the same as or different from the above resin to the kneaded product. In the method for producing a magnetic paint, the magnetic paint is prepared by adding a solvent and a second kneading at a shear stress smaller than the above-mentioned shear stress, wherein the above-mentioned magnetic powder is a magnetic powder having a specific surface area with a BET value of 38 m2/g or more. BET of the above magnetic powder
This is achieved by a method for producing a magnetic paint, characterized in that the first kneading is carried out with the weight of the resin per 1 m'' of the total surface area expressed as Q, 004 g or more. Although various compositions can be used, examples of preferable compositions are shown below: Magnetic powder 100 parts by weight Vinyl resin such as PVB 1.5 to 30 parts by weight Epoxy resin
10-70 parts by weight phenolic resin
10-70 parts by weight Solvent 300-8
If necessary, a composition in which 0.1 to 15 parts by weight of a filler such as alumina or 2 to 30 parts by weight of another resin such as polyurethane is added to this composition can also be applied. In the first kneading, kneading is preferably carried out using, for example, a kneader in order to perform kneading with a large shear stress. Large abrasion stress is 10 to 400 kg/cm
A range of "20 to 300 kg/am" is more preferable. This is because there is a slight tendency for the resin to deteriorate due to mechanical action if kneaded for a long time with the abrasion stress exceeding 300 kg/cm2, and this tendency increases somewhat when the abrasion stress exceeds 400 kg/cm2. When manufacturing magnetic paint, it is preferable to knead magnetic powder, epoxy resin, and refrigerant in the first kneading step.In this case, 10 to 40 parts by weight of epoxy resin should be added to 100 parts by weight of magnetic powder. It is preferable that the amount of epoxy resin is 20.5 parts by weight or more, and it is particularly preferable that the amount of epoxy resin is 20.5 parts by weight or more.If more epoxy resin is required in the composition of the final magnetic coating, the insufficient amount is added in the second kneading process. of epoxy resin may be added.The amount of solvent may be determined as appropriate to achieve the abrasion stress within the above range.
It is sufficient to add about 60 parts by weight. Since the abrasive stress is determined by various factors such as the rotation speed of the kneader blade and the distance between the blade and the container in addition to the viscosity of the mixture, in order to achieve the abrasive stress within the above range, The preferred amount of solvent may vary widely from the above ranges. If a filler is required, the filler may be added and kneaded during the first kneading process, or a separate dispersion treatment may be performed to perform the second kneading process.
It may be added during kneading, and any method may be used. In the present invention, it is preferable to use a magnetic powder having a specific surface area with a BET value of about 38 m2/g or more as the magnetic powder having a large specific surface area. In addition, the amount of resin when performing the first kneading is such that the weight of the resin is 0.0 per m2 of the total surface area expressed by the 73ET value of the magnetic powder.
The total surface area expressed by the BET value of the magnetic powder, which is preferably 0.4 g or more, is the value obtained by multiplying the BET value by the amount (g number) of the magnetic powder. A method for manufacturing a magnetic recording medium using the above-described magnetic paint is to apply the magnetic paint to a substrate, orient it in a magnetic field, and harden it by heating. Although the coating film is preferably oriented in a magnetic field, it does not have to be oriented in a magnetic field. [Operation] Magnetic powder adsorbs resin, which is a polymeric binder, and maintains a dispersed state as a magnetic paint. If the ratio of the amounts of magnetic powder and resin is constant, when magnetic powder with a large specific surface area is used, the amount of resin adsorbed to the magnetic powder will decrease per unit surface area. As a result, the repulsive force caused by the adsorbing resin that had been blocking the magnetic attraction of the magnetic powder decreases, causing agglomeration of the magnetic powder, and the properties of the coating film formed using the paint in such a state deteriorate. However, by increasing the amount of resin used in the initial process of dispersing magnetic powder as the specific surface area of the magnetic powder increases, and by keeping the amount of adsorbed resin on the surface of the magnetic powder almost constant per unit area, It is possible to prevent the agglomeration of particles and obtain a paint in which magnetic powder is uniformly dispersed. Coating films produced using such paints have excellent properties. [Example] Examples are shown below. Example 1 Epoxy resin 0.66 kg, magnetic powder (BET value 38 m"
/g) and 0.27 kg of single-crystal alumina were put into a kneader mixer, and the mixing was carried out for about 15 minutes. Next, 2.2 kg of cyclohexanone was gradually added to the kneader.
Kneading is carried out for 4 hours while applying a shear stress of about 50 kg/cm2. During this time, even if the kneading conditions remain the same, the viscosity of the mixture changes and the abrasion stress increases to 100 kg/am2 or more, but eventually reaches about 100 kg/cm2. Approximately 90% of this mixed material was weighed and placed in a ball mill pot, cyclohexanone was added, and ball mill kneading was carried out for 7 days. Next, the remaining amount of epoxy resin, phenol resin, polyvinyl butyral (abbreviated as PVB in the table), and a mixed solvent of cyclohexanone and isophorone were added to the mixture and mixed in a ball mill so that the weight ratio of the entire composition was as shown in Table 1. A magnetic paint was obtained by kneading. Table 1 Magnetic powder 55 parts by weight Single crystal alumina 5 parts by weight Epoxy resin 17.6
Part by weight Phenol resin 17.6 Part by weight PVB
4.8 parts by weight Next, this paint was spin-coated onto an aluminum disk whose surface had been cleaned in advance, oriented in a magnetic field by a well-known method, and cured at 220° C. to obtain a magnetic disk. The film thickness of the coating film of this magnetic disk was 0.9 μIn, and the surface roughness was Ra=0.04. This magnetic disk was further polished and coated with perfluoroalkyl polyether as a lubricant. The electrical characteristics of this magnetic disk include reduced noise and improved S/N ratio compared to conventional magnetic disks. Examples 2 and 3 Magnetic disks were manufactured using magnetic powders having different BET values. In this case, change the amount of epoxy resin during kneader kneading as shown in Table 2. If the amount of epoxy resin is increased, the amount of epoxy resin in the subsequent ball mill kneading is reduced to maintain the final composition. The composition was adjusted to have the composition shown in Table 1, and the rest was the same as in Example 1. Table 2 also shows the composition of Example 1. Further, Table 1 shows the composition of the magnetic paint produced as a comparative example when kneaded in a kneader. In the case of the comparative example as well, the final composition ratio was adjusted to be the same as in Example 1, and the other components were manufactured using the same method. The surface roughness of the coating film of the manufactured magnetic disk is shown in Example 1 and Table 2. Magnetic powder BET value (+n2/g) Magnetic powder (kg) Epoxy resin (kg) Ratio (resin/magnetic powder) Amount of resin per unit surface area (g) 3.0 0.66 0.22 o, oosg 3, O o , 72 0.24 0.0055 3.0 0.76 0.25 0.0053 Table 3 Comparative example No I H■Magnetic powder B
ET value (m”/g) 28 38 48 Magnetic powder (kg) 3.0 3.0 3.0 Epoxy resin (kg) 0,36 0.36 0
．． 36 ratio (resin/magnetic powder) 0.12.0.1
2 As seen in Table 0.12 and the figure, when magnetic powder with a small specific surface area was used, the surface roughness of the coating film of the magnetic disk manufactured in the comparative example was also good, but when magnetic powder with a large specific surface area was used, the surface roughness of the coating film was good. When using , the surface roughness deteriorates. on the other hand,
In the case of this example, the surface roughness of the coating film obtained was good even when magnetic powder with a large specific surface area was used. Furthermore, in the present invention, it is also possible to form a thin coating film with good surface roughness, for example, a coating film with a thickness of 089 μm or less. In the case of the comparative example, a uniform coating film could not be obtained unless the film thickness was approximately 1 μm or more. Effect of the invention 1 According to the present invention, by manufacturing a magnetic paint by using magnetic powder with a large specific surface area and adjusting the amount of resin in the process of dispersing the magnetic powder, uniform characteristics can be obtained from this magnetic paint. A magnetic recording medium with an excellent coating film could be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the surface roughness of a coating film of a magnetic disk for explaining the present invention.

Claims (1)

[Claims] 1. At least the magnetic powder and resin are first
A magnetic paint is obtained by kneading the mixture to obtain a kneaded product, and then adding at least one type of resin that is the same as or different from the above resin and a solvent to the kneaded product and performing a second kneading at a shear stress smaller than the above-mentioned shear stress to obtain a magnetic paint. In the method for producing a coating material, the magnetic powder is a magnetic powder having a specific surface area with a BET value of 38 m^2/g or more, and the above resin per 1 m^2 of the total surface area expressed by the BET value of the magnetic powder. A method for producing a magnetic paint, characterized in that the first kneading is performed with a weight of 0.004 g or more.