JPH0341892B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a tape-shaped magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium in which magnetic field alignment treatment is performed reliably and stably. Recently, high-density recording is required in magnetic recording. High-density recording can be achieved by improving magnetic recording/reproducing devices and recording methods, but it can also be achieved by improving magnetic recording media. Improving electromagnetic conversion characteristics is known as an example of improving magnetic recording media to achieve high-density recording.
In particular, it is known that it is effective to increase the residual magnetic flux density (Br) and coercive force (Hc) of the magnetic layer and to improve the squareness (squareness) of the magnetic hysteresis curve. As a general magnetic recording medium, so-called magnetic tape is known as a long, strip-shaped non-magnetic support coated with a magnetic coating liquid made by dispersing fine ferromagnetic powder in a binder dissolved in a solvent. As a method for improving the squareness of this type of magnetic recording medium, a method is known in which an external magnetic field is applied to the magnetic recording medium to orient the axis of easy magnetization of the ferromagnetic fine powder in a desired direction. ing. For example, as shown in FIG. 1, a specific technique for performing magnetic field orientation treatment on such a tape-shaped magnetic recording medium is as follows: As shown in FIG. A magnetic coating solution 5 is applied to a long, strip-shaped non-magnetic support 3 using a coating head 4 to form a coating film 5', and then a layer is placed downstream of the coating head 4 in the support transport direction. The coating film 5' is subjected to a magnetic field orientation treatment by the disposed orientation magnet 6, and then the coating film 5' is dried and solidified by the drying means 7 disposed downstream of the orientation magnet 6 to form a magnetic layer. The technology is known. Further, as shown in FIG. 2, the orientation magnet 6 is
It is also known that the device is placed inside the device. Details of such technology can be found in, for example, Japanese Patent Publication No. 45-21547,
It is described in Publications No. 52-2602, No. 58-84706, etc. However, it has been extremely difficult to obtain a magnetic recording medium with sufficient squareness using the conventional methods as described above. That is, in the method shown in FIG.
The easy magnetization axis of the ferromagnetic fine powder is difficult to be oriented by the orientation magnet 6 because the coating film tends to dry before being transferred to the drying means 7 after passing through the orientation magnet 6. During this period, the axis of easy magnetization, once oriented, tends to return to the non-oriented state. In addition, in the method shown in Figure 2, since the drying process is performed immediately after the orientation process, it is difficult for the easily magnetized axis to return to its original non-oriented state once it has been oriented. Problems occur in the same manner as in the method of FIG. 1 above. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a magnetic recording medium in which magnetic field orientation is performed reliably and stably, and a magnetic layer with high squareness can be formed. The purpose is to The present invention has been made based on the knowledge that the success or failure of the magnetic field orientation is largely controlled by the viscosity of the magnetic coating liquid immediately before the magnetic field orientation treatment, and the method for producing a magnetic recording medium of the present invention continuously The drying means is provided with a coating means for applying the above-described magnetic coating liquid onto the strip-shaped non-magnetic support that is transferred to the drying means, and the magnetic coating liquid is applied within the drying means. The solvent contained in the layered coating film is 210 to 500 parts by weight per 100 parts by weight of the ferromagnetic fine powder.
After controlling the evaporation concentration of the solvent by the drying means so as to account for parts by weight, the ferromagnetic fine powder in the coating film is orientated in a predetermined direction by a magnetic field orienting means disposed within the drying means. , drying the coating film,
It is characterized by solidification. Through research conducted by the present inventors, it has been confirmed that magnetic field orientation can be reliably performed when magnetic field orientation treatment is performed while maintaining the composition of the magnetic coating film as described above. A coating means and a magnetic field orientation means are provided in the drying means, and the composition of the coating film is set by controlling the drying means, and the magnetic field orientation is performed immediately after applying the magnetic coating liquid. The coating film does not dry before the orientation treatment and the composition does not change, and the magnetic field orientation treatment is always stably performed on the coating film having the composition described above. Furthermore, since the magnetic field orientation is carried out within the drying means, the coating film subjected to the magnetic field orientation treatment immediately dries and solidifies, making it difficult for the ferromagnetic fine powder, once oriented, to return to its non-oriented state. . Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows an example of an apparatus for carrying out the method of manufacturing a magnetic recording medium of the present invention. In the apparatus shown in FIG. 3, the non-magnetic support 3 is sent out from the delivery roll 1, continuously transported, and wound onto the take-up roll 2, as in the apparatus shown in FIG. 2 described above. The continuously transported non-magnetic support 3 passes through two adjacent drying means 17, 27. These drying means 17 and 27 each have a drying air inlet 17 through which drying air is introduced.
a, 27a and chambers 17c, 27c, each having a drying air inlet 1
For example, heating parts of steam heaters 18 and 28 are disposed in the passages communicating with chambers 17c and 27a, and these heaters 18 and 28 cause the chambers 17c and 27 to be heated.
Drying air is blown into the chamber c. A coating head 4 and an orientation magnet 6 disposed downstream of the head 4 are provided in the drying means 27 on the upstream side in the transport direction of the long, strip-shaped nonmagnetic support 3.
A control valve 26 is interposed in a steam pipe 29 that supplies heating steam to a steam heater 28 for the drying means 27. A magnetic coating liquid 5 is applied to the surface (upper surface in the figure) of the non-magnetic support 3 that is continuously transferred by the coating head 4, and the coating film 5' is applied to the drying means 1.
The magnetic layer is dried and solidified by steps 7 and 27 to form a magnetic layer. The magnetic coating liquid 5 is made by dispersing ferromagnetic fine powder in a binder dissolved in a solvent. The ferromagnetic fine powder used in the present invention includes γ-Fe ₂ O ₃ , Co Containing γ-Fe ₂ O ₃ ,
Known ferromagnetic fine powders such as Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , Co-Ni-P alloy, Co-Ni-Fe alloy can be used. No. Publication,
Special Publication No. 18372, No. 47-22062, Publication No. 22513, Special Publication No. 28466, Publication No. 38755, No. 4286
Publication No. 12422, Special Publication No. 12422, Special Publication No. 12422, Special Publication No. 1977-
Publication No. 17284, Special Publication No. 18509, Publication No. 18509, Special Publication No. 18509
-Described in Publication No. 18573, etc. As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, ultraviolet curable resins, electron beam curable resins, and mixtures thereof are used. As a thermoplastic resin, the softening temperature is 150℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
500, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer,
Vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic Acid ester styrene copolymer, urethane elastomer,
Nylon - silicone resin, nitrocellulose -
Polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.) ), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof. Examples of these resins are given in Japanese Patent Publication No. 37-6877, 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-20907
No. 41-9463, 41-14059, 41-16985, 42
-6428, 42-11621, 43-4623, 43-15206
No. 44-2889, No. 44-17947, No. 44-18232, 45
−114020, 45−14500, 47−18573, 47−
No. 22063, No. 47-22064, No. 47-22068, No. 47-22069
No. 47-22070, No. 47-27866, etc. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, but when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, examples include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, epoxy-polyamide resins, nitrocellulose melamine resins, high molecular weight polyester resins, and isocyanate resins. Mixtures of polymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamide resins and A mixture, etc. Examples of these resins are given in Japanese Patent Publication No. 39-8103, 40-
No. 9779, No. 41-7192, No. 41-8016, No. 41-14275,
No. 42-18179, No. 43-12081, No. 44-28023, 45-
No. 14501, No. 45-24902, No. 46-13103, No. 47-22065
No. 47-22066, No. 47-22067, No. 47-22072,
No. 47-22073, No. 47-28045, No. 47-28048, 47-
This has been published in publications such as No. 28922. These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic fine powder and the binder is set in the range of 10 to 200 parts by weight of the binder to 100 parts by weight of the ferromagnetic fine powder. Additives include dispersants, lubricants, abrasives, and the like. The organic solvents used during dispersion, kneading, and coating include acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propanol, and butanol, and methyl acetate, ethyl acetate, acetic acid. Ester systems such as butyl, ethyl lactate, glycol acetate, and monoethyl ether: Ether, glycol ether systems such as glycol dimethyl ether, glycol monoethyl ether, and dioxane: Tar systems (aromatic hydrocarbons) such as benzene, toluene, and xylene: Methylene Chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, dichlorobenzene, etc. can be used. The non-magnetic support 3 preferably has a thickness of about 2.5 to 100 microns, preferably about 3 to 40 microns. Materials used include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, plastics such as polycarbonate, and aluminum. , metals such as copper, ceramics such as glass, etc. may also be used. Methods for applying the magnetic coating liquid 5 onto the support 3 include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Spray coating etc. can be used, and other methods are also possible, and detailed explanations of these methods are given in "Coating Engineering" published by Asakura Shoten, pages 253 to 277 (published on March 20, 1972). As the orientation magnet 6, both an electric magnet using a solenoid coil or a permanent magnet can be used, and various arrangements are possible in order to effectively orient the axis of easy magnetization of the ferromagnetic fine powder. Next, a detailed example will be described in which a magnetic recording material was manufactured using the apparatus shown in FIG. 3 by selecting and using a specific material from the materials described above. [First Example] The following composition was placed in a ball mill and thoroughly kneaded, and then Desmodyur L-75 (trade name of a polyisocyanate compound manufactured by Bayer) 2 was added as a binder.
Parts by weight (hereinafter referred to as parts) were added and uniformly mixed and dispersed to obtain a magnetic coating liquid 5. Co-containing -γ-Fe ₂ O ₃ powder (ferromagnetic fine powder) (Nitrogen adsorption specific surface area 30 m ² /g) 100 parts Nitrocellulose (binder) 10 parts Polyurethane: Molecular weight approximately 30,000 (binder) 10 parts Vinyl chloride -Vinyl acetate-vinyl alcohol copolymer (binder) 10 parts myristic acid (lubricant) 2 parts lecithin (lubricant) 1 part n-butyl acetate (solvent) 220 parts Polyester film was used as the non-magnetic support 3 Then, the magnetic coating liquid 5 was coated on the surface of the non-magnetic support 3, which was continuously transported, using the coating head 4. The orientation magnet 6 used has a magnetic flux density of 1000 Gauss and a length of 1 m, and the coating speed is 50 m/min (that is, the residence time of the coating film 5' in the orientation magnet 6 is 2 × 10 ^-2
minutes). The coating film 5' applied to the surface of the non-magnetic support 3 is dried by the drying means 17, 27.
The evaporation concentration of the solvent is controlled by controlling the control valve 26 that operates the drying air temperature, so that the solvent in the coating film 5' just before entering the orientation magnet 6 is equal to 100 parts of the ferromagnetic fine powder. The amount was set to 220 parts (that is, so that almost no solvent evaporated between the coating head 4 and the orientation magnet 6). As described above, a magnetic tape was produced in which the coating film 5' was solidified on the surface of the nonmagnetic support 3 and a magnetic layer was formed thereon. Next, the magnetic tape was subjected to a mirror polishing process, and then cut into 1/2 inch width samples.
The squareness ratio (SQ) in the horizontal direction was measured.
This squareness ratio is the value obtained by dividing the residual magnetic flux density (Br) by the saturation magnetic flux density (Bm). As comparative samples, magnetic tapes (sample No. 1 and 2) were prepared using the apparatus shown in FIGS. 2 and No. 3) were prepared, and the squareness ratio was measured in the same manner. The results of these measurements are shown in Table 1 below.

[Second example]

After putting the following composition into a ball mill and thoroughly kneading it, we added Desmodyur L75 (trade name of a polyisocyanate compound manufactured by Bayer) as a binder.
8 parts were added and uniformly mixed and dispersed to obtain magnetic coating liquid 5. Co-containing - γ-Fe ₂ O ₃ (ferromagnetic fine powder) 100 parts (nitrogen adsorption specific surface area 30 m ² /g) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (binder) 10 parts epoxy resin (bond (agent) 10 parts dimethylpolysiloxane (lubricant) 1 part (25°C viscosity 1000 cs) Butyl palmitate (lubricant) 1 part Al ₂ O ₃ (abrasive) 6 parts n-butyl acetate (solvent) X part n of solvent - 160 and 180 parts of butyl acetate, respectively.
Six kinds of magnetic coating liquids 5 were prepared as 1 part, 200 parts, 215 parts, 222 parts, and 230 parts, and these magnetic coating liquids 5 were
Using the apparatus shown in FIG. 3 and setting the same coating conditions as in the first example, the magnetic tape was coated on a non-magnetic support 3 made of polyester film to obtain a magnetic tape. The solvent evaporation concentration was controlled by the control valve 26 in the drying means 27, as in the first embodiment, so that almost no solvent evaporated between the coating head 4 and the orientation magnet 6. The six types of magnetic tapes obtained as described above were each subjected to a mirror polishing process, and then cut into 1/2 inch widths to prepare samples No. 4 to No. 9, and the squareness ratio of each was measured. did. The results are shown in Table 2 below.

【table】

[Third example]

The following composition was placed in a ball mill and thoroughly kneaded, and then added with Desmodyur L-75 (trade name of a polyisocyanate compound manufactured by Bayer) 5 as a binder.
of the mixture was added and uniformly mixed and dispersed to obtain a magnetic coating liquid 5. Co-containing -γ-Fe ₂ O ₃ powder (ferromagnetic fine powder) 100 parts (Nitrogen adsorption specific surface area 35 m ² /g) Nitrocellulose (binder) 10 parts Polyurethane: Molecular weight approximately 30,000 (binder) 10 parts Vinyl chloride -Vinyl acetate-vinyl alcohol copolymer (binder) 10 parts stearic acid (lubricant) 2 parts dimethylpolysiloxane (lubricant) 0.5 parts (100 cp) n-butyl acetate (solvent) 200 parts cyclohexane (solvent) 30 Section This magnetic coating liquid 5 was coated on a non-magnetic support 3 made of a polyester film using the apparatus shown in FIG. 3 under the same coating conditions as in the first embodiment to obtain a magnetic tape. The solvent evaporation concentration was controlled by the control valve 26 in the drying means 27, as in the first embodiment, so that almost no solvent evaporated between the coating head 4 and the orientation magnet 6. And as the orientation magnet 6, the average magnetic flux density is 1500.
Using a Gaussian S-N opposing permanent magnet with a length of 1 m,
By changing the transfer speed of the non-magnetic support 3, that is, the coating speed of the coating liquid 5, the orientation magnet 6 of the coating film 5' can be adjusted.
Five types of samples were prepared by setting the residence time in five different ways as shown below, and the squareness ratio of each sample was measured. The residence time of the coating film 5' in the orientation magnet 6 was determined by dividing the length of the orientation magnet 6 by the support transport speed. The measurement results of the squareness ratio are shown in Table 3 below.

[Table] As is clear from Table 3, even if the amount of solvent in the coating film 5' during the magnetic field orientation treatment is set to 210 parts by weight or more per 100 parts by weight of the ferromagnetic fine powder, the coating film 5' If the residence time of the coating film 5' in the magnetic field is set to a small value, the squareness ratio may fall below 0.9, so it is desirable to set the residence time of the coating film 5' in the magnetic field to approximately 9×10 ^-3 minutes or more. The residence time of the coating film 5' in the magnetic field can be increased by setting the coating speed to a low value; however, in the production of normal commercial magnetic recording media, if the coating speed is set too low, the productivity will be reduced. Therefore, the coating speed should be at least 50 m/min.
It is preferable to set the time to about a minute. In the first to third embodiments described above, the drying means 27 is controlled so that almost no solvent evaporates between the coating head 4 and the orientation magnet 6. The drying means 27 may be controlled so that the solvent is evaporated to a certain extent, and as a result, the amount of solvent in the coating film 5' is set within the above-mentioned range immediately before entering the orientation magnet 6. Further, in the apparatus shown in FIG. 3, the coating head 4 is arranged close to the orientation magnet 6, but as shown in FIG.
b, chamber 27c, heater 28, steam pipe 29,
Dry air inlet 37a similar to control valve 26, exhaust port 37b, chamber 37c, heater 38, steam pipe 3
9. A drying means 37 having a control valve 36 is installed apart from the drying means 27 in which the orientation magnet 6 is disposed, and a coating head 4 is installed within this drying means 37.
is arranged, and by controlling both the drying means 37 and the drying means 27, the coating film 5' immediately before entering the orientation magnet 6 is
The amount of solvent may be set to a desired value. As explained in detail above, according to the method of the present invention,
This provides a magnetic recording medium that has an extremely high squareness ratio and can meet the demands for high-density recording.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of an apparatus for implementing the conventional method for manufacturing magnetic recording media, FIG. 3 is a schematic diagram showing an example of an apparatus for implementing the method of the present invention, and FIG. 4 is a schematic diagram for implementing the method of the present invention. FIG. 2 is a schematic diagram showing another example of a device for 1... Delivery roll, 2... Winding roll, 3
...Nonmagnetic support, 4...Coating head, 5...Magnetic coating liquid, 5'...Coating film, 6...Orienting magnet, 7,
17, 27, 37...Drying means, 18, 28, 3
8... Heater, 26, 36... Control valve.

Claims (1)

[Scope of Claims] 1. A magnetic coating liquid consisting of fine ferromagnetic powder dispersed in a binder dissolved in a solvent is placed on a continuously transported strip-shaped non-magnetic support in a drying means. The evaporation concentration of the solvent was adjusted as above so that the solvent contained in the coating film layered on the support was 210 to 500 parts by weight per 100 parts by weight of the ferromagnetic fine powder. While controlling by drying means,
A method for producing a magnetic recording medium, which comprises orienting the ferromagnetic fine powder in the coating film in a predetermined direction using a magnetic field orientation means disposed within the drying means, and then drying and solidifying the coating film. . 2. The coating speed of the coating solution is 50 m/min or more, and the residence time of the coating film in the magnetic field orientation means is 9.
2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the time is 10 ^-3 minutes or more.