JPH04258812A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease drop-outs by forming a magnetic layer on a nonmagnetic base, then subjecting the surface of the magnetic layer to a smoothing treatment by using calender rolls constituted by sticking a lubricant onto the surfaces of specular surface metallic rolls. CONSTITUTION:The magnetic layer is formed by applying a magnetic coating material on a polyester film, etc., and drying the coating. The surface smoothing treatment of the magnetic layer is then continuously executed by using the calender rolls alternately disposed with the specular surface metallic rolls and the elastic rolls. The fluorine-based lubricant dissolved in fluorocarbon is continuously sprayed in the form of mist on the surfaces of the specular surface metallic rolls at this time. A back coat layer is thereafter formed on the rear surface side. The contamination of the calender rolls with lapse of time is prevented in this way and the drop-outs are decreased; in addition, the durability is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic disks having a magnetic layer on a non-magnetic support.

0002

[Prior Art] This type of magnetic recording medium is made by coating a magnetic paint on a non-magnetic support such as a polyester film and drying it to form a magnetic layer, and then smoothing the surface of this magnetic layer using a calendar roll. It is produced by chemical treatment.

[0003] The above-mentioned calender roll is composed of a plurality of mirror-finished metal rolls and elastic rolls arranged alternately, and between these rolls, the magnetic layer side formed by coating and drying is in contact with the mirror-finished metal roll. The magnetic layer and the support are made to run, and in order to obtain a sufficient smoothing effect, a considerable amount of roll pressure is applied to the magnetic layer running in the gap between the rolls. In addition, the roll itself is a hot roll so that this magnetic layer is thermally softened.

0004

[Problems to be Solved by the Invention] However, in such smoothing treatment using heating and pressure, some components of the magnetic layer adhere to the surface of the mirror-finished metal roll that comes into contact with the magnetic layer over time. As a result, the roll surface gradually becomes dirty.
This contamination causes concave defects on the surface of the magnetic layer, resulting in frequent dropouts.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional circumstances, it is an object of the present invention to prevent a calender roll from becoming dirty over time and to obtain a magnetic recording medium with less dropout.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the inventors have made extensive studies and found that if the surface of a mirror-finished metal roll is smoothed with a lubricant attached to it, The present invention was completed based on the knowledge that staining of the roll surface over time can be significantly suppressed and a magnetic recording medium with less dropouts can be obtained.

That is, in the present invention, a magnetic coating is coated on a non-magnetic support and dried to form a magnetic layer, and then the surface of the magnetic layer is coated with a calender roll having a lubricant adhered to the surface of a mirror-finished metal roll. The present invention relates to a method for manufacturing a magnetic recording medium, which is characterized by subjecting the magnetic recording medium to smoothing treatment.

[0008]

[Structure and operation of the invention] The calender roll used in the present invention is made up of mirror-finished metal rolls and elastic rolls arranged alternately, and the structure of each roll itself is no different from the conventional one. You can use the existing one as is. Although the number of rolls can be selected as appropriate, it is generally preferable that the total number of rolls is 5 to 9.

The present invention is characterized in that when smoothing the surface of the magnetic layer using such a calender roll, a lubricant is applied to the surface of the mirror-finished metal roll that comes into contact with the magnetic layer. This lubricant can be attached by any suitable method depending on the type of lubricant. For example, a solution of a lubricant dissolved in an organic solvent is prepared, and the solution is sprayed onto the roll surface in the form of a mist to form a lubricating layer. The formation of such a lubricant layer may be performed prior to the smoothing treatment of the magnetic layer, or may be performed simultaneously with the smoothing treatment, that is, by spraying the lubricant continuously or intermittently while performing the smoothing treatment. You can go there.

[0010] The type of lubricant used is not particularly limited;
Any of the various lubricants conventionally known as additives to magnetic paints or as top coats on the surface of magnetic layers can be used. Among these, fluorine-based lubricants and liquid paraffin are recommended as the most preferred.

[0011] According to the calender roll to which such a lubricant is adhered, the application,
When the dried magnetic layer is heated and softened by the roll and pressed into a certain shape, the presence of the lubricant prevents a portion of the magnetic layer from adhering to the roll surface, and it lasts for a long time. A beautiful surface with a mirror shine can be maintained. As a result, no concave defects due to the above-mentioned transfer are observed on the surface of the magnetic layer, an ideal surface smoothing effect is achieved, and a magnetic recording medium of good quality with less dropouts is obtained.

In addition, in the above smoothing treatment, a part of the lubricant on the roll surface is transferred to the surface of the magnetic layer, and this lubricant also fills the internal pores (opened due to thermal softening) of the magnetic layer. A phenomenon called being press-fit occurs. Therefore,
After this smoothing treatment, it is possible to omit the formation of a top coat layer of lubricant, which has been generally employed in the past, and moreover, it is difficult to fill the lubricant deep into the magnetic layer with the formation of the conventional top coat layer. (Because the internal pores are normally closed), this can be easily achieved by press-fitting into the internal pores, so the durability as a magnetic recording medium is significantly improved. .

[0013] In the present invention, the magnetic layer to be subjected to the above-mentioned smoothing treatment is usually formed by coating a magnetic coating material on a non-magnetic support such as a polyester film by a conventional method and drying it to a thickness of 0.5 to 0. It is about 4.0 μm. Even if this magnetic layer is provided on one side of the non-magnetic support,
It may be provided on both sides. In the case of both sides, the smoothing process is applied to each side. In the case of one side, a back coat layer is usually formed on the opposite side.

Magnetic paints usually contain magnetic powder, a binder, and a dispersion medium for these, and if necessary, various known additives such as a dispersant, an antistatic agent, an abrasive, a lubricant, etc. are kneaded therein. The dispersion medium includes not only organic solvents but also water and other aqueous media.

[0015] As the magnetic powder, γ-Fe2O3, Fe
Conventional magnetic powders include acicular oxide magnetic powders such as 3O4, Co-containing γ-Fe2O3, and CrO2, plate-shaped ferrite magnetic powders such as Ba, Sr, and Pb ferrites, and metal magnetic powders such as Fe, Ni, Co, and alloys thereof. Any known material can be used.

As the binder, vinyl chloride-vinyl acetate copolymer, cellulose resin, polyurethane resin, acrylonitrile-butadiene rubber, styrene-butadiene rubber, polyester resin, polyamide resin, polyvinyl butyral resin, As a crosslinking agent, any of those conventionally known for use in magnetic layers of magnetic recording media, such as isocyanate compounds and radiation-curable resins, can be used, and two or more of these may be used in combination.

[0017]

As described above, according to the present invention, it is possible to prevent the calender roll from becoming dirty over time, thereby making it possible to produce a magnetic recording medium with less dropout. This medium also has the advantage of being extremely durable due to the lubricant transferred from the roll surface and press-fitted into the magnetic layer.

[0018]

EXAMPLES Next, examples of the present invention will be described in more detail. In addition, in the following, parts mean parts by weight.

Example 1 Ferromagnetic metallic iron powder (coercive force 1600 oersted, saturation magnetization Amount 125 emu/g, average major axis diameter 0.18 μ
m, average axial ratio 10) 100 parts, hydroxyl group-containing vinyl chloride resin with a degree of polymerization 400 (Eslec E manufactured by Sekisui Chemical Co., Ltd.) 1
2 parts, thermoplastic polyurethane resin (number average molecular weight 20,000,
glass transition temperature 25°C), 7 parts of aluminum oxide powder with an average particle size of 0.2 μm, α- with an average particle size of 0.8 μm
After kneading and dispersing 4 parts of Fe2O3 powder, 1 part of carbon black (trade name: HS-500, manufactured by Asahi Carbon Co., Ltd., manufactured by Asahi Carbon Co., Ltd.), 25 parts of cyclohexanone, 25 parts of toluene, and 25 parts of methyl ethyl ketone in a ball mill for 120 hours, In addition, 2.5 parts of myristic acid, 1.5 parts of industrial n-butyl stearate, and 0.5 parts of liquid paraffin.
1 part, and 5 parts of a trifunctional polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) were added and mixed with stirring to prepare a magnetic paint.

Next, this magnetic paint was coated on one side of a biaxially oriented polyethylene terephthalate film having a thickness of 10 μm to a thickness of 3 μm after drying, and dried to form a magnetic layer. After that, the surface of the magnetic layer is smoothed by using calender rolls (total number of rolls: 7) consisting of alternating mirror-finished metal rolls and elastic rolls.
The test was carried out continuously over a distance of 1,000 m. At that time, a fluorine-based lubricant (trade name: FUONBLIN Z DEAL manufactured by Enimon Co., Ltd.) dissolved in Freon was applied to the surface of the mirror-finished metal roll.
) was made into a mist and sprayed continuously.

After smoothing the surface of the magnetic layer in this way, carbon black (trade name: SEAST 5H, manufactured by Tokai Carbon Co., Ltd., manufactured by Tokai Carbon Co., Ltd.) with an average particle diameter of 20 mμ is coated on the back side of the magnetic layer.
) 60 parts, 7.5 parts of carbon black with an average particle size of 75 μm (trade name HS-500, manufactured by Asahi Carbon Co., Ltd.), 30 parts of calcium carbonate powder with an average particle size of 0.05 μm, 45 parts of thermoplastic polyurethane resin, nitrocellulose 40 parts, 15 parts of trifunctional polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.), 3 parts of cyclohexanone
A back coat paint made by kneading and dispersing 30 parts of toluene and 330 parts of toluene in a ball mill for 96 hours was applied to a dry thickness of 1.0 μm, dried, and cured at 60°C for 20 hours (cure). A back coat layer was formed.

[0022] The magnetic tape original fabric obtained in this way (
A magnetic tape was produced by cutting the tape (total length: 4000 m, total thickness: 13 μm) into 1/7 inch width.

Example 2 The same procedure as in Example 1 was carried out, except that liquid paraffin dissolved in hexane was used instead of the fluorine-based lubricant dissolved in Freon for the surface smoothing treatment of the magnetic layer. A magnetic tape with a total length of 4000 m was produced.

Comparative Example 1 A magnetic tape with a total length of 4000 m was produced in the same manner as in Example 1, except that the fluorine-based lubricant dissolved in Freon was not sprayed onto the roll surface during the surface smoothing treatment of the magnetic layer. .

Each of the magnetic tapes of the above examples and comparative examples was stored in a DAT cassette, and this cassette was loaded into a DAT deck DTC-1000ES manufactured by Sony Corporation, and a 400 Hz sine wave was recorded. Size dropout was measured. In addition, as an evaluation of durability, the amount of deterioration in RF output was measured by the following method. These results are shown in Table 1 below.

<Deterioration amount of RF output> The electric signal taken out from the RF output terminal on the circuit board in the DAT deck is recorded by a recorder. The running conditions were to play a certain point on the tape for 1 minute and rewind it 5000 times in an environment of 20°C and 60% RH, and the RF output A at the first run and the RF output B at the 5000th run. Measure. The amount of deterioration of the RF output is calculated by 20log(B/A) and expressed in dB.

[0027]

[Table 1]

As is clear from the results in Table 1 above,
According to the method of the present invention, it is possible to prevent the occurrence of concave defects on the surface of the magnetic layer due to dirt on the calender roll.
It is possible to obtain magnetic tape with less dropout,
Furthermore, it can be seen that this magnetic tape is also extremely durable.

Claims (2)

[Claims] Claim 1: After coating a magnetic paint on a non-magnetic support and drying it to form a magnetic layer, the surface of the magnetic layer is smoothed using a calender roll with a lubricant attached to the surface of a mirror-finished metal roll. A method for manufacturing a magnetic recording medium, characterized by: 2. The method for producing a magnetic recording medium according to claim 1, wherein the lubricant is a fluorine-based lubricant or liquid paraffin.