JPH0253221A - Magnetic recording medium using water base coating material containing magnetic powder and its manufacture - Google Patents

Abstract

PURPOSE:To realize high dispersibility of magnetic powder without using a dispersing agent and to obtain a magnetic recording medium with high recording density by using such a magnetic powder coated with alternate copolymer of polyoxyethylene allylmethyldiether and maleic anhydride. CONSTITUTION:The water-base coating material containing magnetic powder consists of acrylic resin and water as the main components and contains the magnetic powder dispersed therein, the particles of which are coated with alternate copolymer of polyoxyethylene allylmethyldiether and maleic anhydride. The water-base coating material is applied on the surface of a substrate and dried to give a coating-type magnetic layer. Thereby, the magnetic powder is highly dispersed in the water-base coating material without addition of a dispersing agent, and the magnetic recording medium having high performance and excellent recording density can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a magnetic recording medium.
It can be easily produced by coating under favorable conditions,
Moreover, the present invention relates to a magnetic recording medium manufactured using a water-based paint containing magnetic powder, which exhibits excellent magnetic properties.

(Prior art) Magnetic recording media manufactured by applying paint containing magnetic powder are widely known, for example as well-known music tapes, and are basically composed of a base film made of polyester or the like. A paint consisting of an inorganic component and an organic component is applied on top to form a magnetic layer.

The main material among the inorganic components constituting the above-mentioned magnetic layer is magnetic powder, but the type differs depending on the application. For example, in low-noise music tapes, standard VTR tapes, etc., fine particles γ
-F6203% high-quality music cassette tapes, VHS, β
For commercial VTR tapes, etc., use Go 7-FeJ3 or Cry, in which part of the Fe is replaced with CO, etc. For high-end cassette tapes, music micro tapes, 8 mm VTR tapes, etc., F is used.
e-metal powder etc. are used. Other inorganic ingredients include surfactants and graphite.

IF anti-static analysis such as carbon black, chromium oxide (cr
20s), alumina (Heko 203), titania (
TiJ).

An abrasive such as silicon carbide (Sin) or α-hematite (α-Fe20.) is used as appropriate.

The organic components contained in the magnetic layer include a binder resin, a hardening agent, a dispersant, a lubricant, and a plasticizer. Examples of the binder resin include vinyl-vinyl acetate copolymer, vinyl chloride vinyl acetate alcohol copolymer, Polyurethane, nitrocellulose, and other materials are often used. In addition, lecithin and surfactants are used as dispersants, higher fatty acids, higher fatty acid esters, silicone oils, fluorinated oils, etc. are used as lubricants, and phthalic acid and higher fatty acids S+' are used as lubricants. ), ff-ster compounds, etc. are used, respectively.

The magnetic tape manufacturing process in which a magnetic layer is formed on a base film consists of a coating process in which a mixture selected from the various materials listed above is dispersed in an organic solvent (usually toluene) to form a coating material, and a paint coating process. The coating process is broadly divided into the coating process, in which the paint made by the process is applied to the surface of a predetermined substrate, and the latter coating process includes a process in which the magnetic powder is passed through a magnetic field to orient it, a drying process in which the applied paint is dried, etc. is included. In addition, in the former coating process, the dispersibility of magnetic powder in organic solvents such as toluene greatly affects the determination of the characteristics of the produced magnetic tape, so improving it is one of the challenges.

In addition, in the conventional manufacturing of magnetic tapes, etc., as mentioned above, organic solvents such as toluene are used in the magnetic powder-containing paint, so there are concerns about the working environment and waste liquid treatment equipment in the paint forming process or coating process. These points need to be taken into consideration, and there are problems in that these points will be reflected in the cost of the product, or the negative impact on the environment may also be an issue.

(Problems to be Solved by the Invention) In general, paints containing highly dispersed magnetic powder can increase the magnetic powder density per unit area of the film tape and can achieve high orientation, thereby increasing the recording density. It is well known that it leads to However, magnetic powder, which is generally used in the form of particles of several tens of νm or less, causes problems such as particle aggregation, and it is not easy to obtain a uniform and highly dispersed state in a solution. In order to improve the dispersibility of magnetic powder in the constituent organic solvents, various dispersants have been tested and used. By the way, when using such a dispersant, on the one hand, the presence of the dispersant in the magnetic layer lowers the density of the magnetic powder, which often results in a decrease in recording density. It is well known.

Therefore, the present inventors have developed a highly functional magnetic recording medium with excellent magnetic recording density by making it possible to achieve high dispersion in a magnetic powder-containing water-based paint without externally adding a dispersant. In order to provide this, we have made extensive research and have come up with the present invention.

That is, one of the objects of the present invention is to provide a water-based paint containing magnetic powder that enables high dispersion of the magnetic powder without using a dispersant, and to provide a water-based paint containing magnetic powder that enables high dispersion of the magnetic powder without using a dispersant.
1. Another object of the present invention is to produce a magnetic recording medium with high magnetic recording density, by replacing the conventional 6-well powder-containing paint with a water-based one. The object of the present invention is to provide a novel method for manufacturing a magnetic recording medium, which makes it possible to improve the working environment, especially in the coating process, and to reduce the need for waste liquid treatment equipment.

Still another object of the invention is to provide a magnetic recording medium in which a coated magnetic layer can be formed that can exhibit a high squareness ratio of 0.9 or more compared to conventional magnetic recording media. .

(Means for Solving the Problems) The magnetic recording medium according to the present invention is characterized by a magnetic recording medium mainly composed of acrylic resin and water, and whose surface is coated with an alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride. A coated magnetic layer is formed by applying a water-based paint containing dispersed magnetic powder onto the surface of a substrate and drying it.

One of the features of the present invention is that the surface of magnetic powder is coated with an alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride, thereby increasing the dispersibility of the magnetic powder in an aqueous solution. The purpose of this invention is to create a water-based paint containing magnetic powder, eliminate the need for a dispersant, and form a dispersant-free magnetic layer on the surface of the substrate after coating.

The alternating copolymer of polyoxyethylene furyl methyl diether and maleic anhydride used for surface coating of such magnetic powder has already been proposed by the present inventors in a patent application filed in 1982.
This is proposed in No.-108458. The alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride used for surface coating of the magnetic powder of the present invention has the following formula, and the molecular weight of the polyoxyethylene allyl methyl diether is approximately 100 to 300,000. In particular, those having a molecular weight of about 1,000 to 20,000 can be preferably used. The alternating copolymerization of polyoxyethylene allylmethyl diether and maleic anhydride can be carried out, for example, by mixing 1,000 of these polymers and carrying out alternating copolymerization by solution polymerization, suspension polymerization, or emulsion polymerization. The alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride preferably has 3 to 10,000 repeating units, preferably 6 to 100 repeating units.To coat the surface of magnetic powder with this alternating copolymer, individual This can be carried out by any suitable method such as the ball mill method, homomixer method, sand mill method, sonication method, etc., but the Dan de mill method is particularly preferred in terms of coating efficiency, etc.
It's gone.

In the present invention, the magnetic powder is not particularly limited, and various conventionally known magnetic powders can be used, examples of which include Fe and 0.4-Fe2O3.

High Hc type 7-Fe2O3 (Fe304), Co-containing 7-Fe203Co coated 7-Fe2O3, ferrite (
MxFe, -xo4: M is Zn, Ni, Mn,
Examples include first transition metals such as Cr and Cd (X is 0 to 1), barium ferrite, and the like. The particle size of the magnetic powder is approximately in the range of 0.1 μm to 0.5 μm, and those within the range conventionally used in the above-mentioned recording medium can be used as is.

The mixing ratio of these magnetic powders and the above surface coating agent is:
Coating material 1-2wH per 1O magnetic powder in weight ratio
In many cases, it is better to set the value within the range of .

The surface-coated magnetic powder used in the present invention exhibits hydrophilicity, and therefore can be dispersed in water to form a water-based paint as described above. Depending on the application, suitable binders, curing agents, lubricants, plasticizers, surfactants, antistatic agents, abrasives, etc. can be added and mixed to this water-based paint containing magnetic powder. One of the features of the present invention is that acrylic resin and water are used as a binder solution.

In the water-based paint containing magnetic powder used in the present invention, it is preferable that the ratio of acrylic resin and water be in the range of 30:70 to 50:50.If the ratio is less than 30N0, water will not easily evaporate and drying will be difficult. If the ratio is 50:50 or more, the amount of acrylic resin is excessive, resulting in a problem that the magnetic powder in the magnetic layer decreases and it is difficult to increase the density.

The above paint is applied to a base material to a thickness of about 3 μm by the following method, and after drying, calendering is performed to smooth the surface.

■Knife coater type that uses the gap between the knife and base to coat ■Reverse roll coater type that uses the rotating direction of several rolls Gravure roll coater type that uses a gravure coater with markings on the surface, etc. This can be carried out by any known method.

In the present invention, a tape-shaped substrate such as a polyester film is used as the base material, and a magnetic recording medium is manufactured as a magnetic recording tape or a floppy disk.

(Effects of the Invention) With the above configuration, the present invention allows the thickness of the magnetic layer coated on the substrate to be extremely thin, and also allows the IIn powder to be highly filled and highly oriented. This has the effect of enabling high-density magnetic recording.

Furthermore, since the magnetic powder can be highly dispersible as a water-based paint, it is possible to improve the working environment and reduce the need for waste liquid treatment equipment, etc., which is effective in reducing the product cost of magnetic recording media and improving the environment.

Furthermore, according to the magnetic recording medium using the water-based paint of the present invention,
This has the effect that a recording medium exhibiting excellent magnetic recording characteristics with a squareness ratio of 0.9 or more can be realized.

(Example) The present invention will be explained below based on test examples and examples.

The mixing ratio of the magnetic powder and the surface coating agent was tested as follows.

Magnetic powder (Fe, O, particle size: 0.2 to 0.4 μm) was mixed with an alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride (molecular weight of polyoxyethylene allyl methyl diether was 1524, Three types of samples were prepared by coating the surface with Unit 8) and setting the ratio of magnetic powder (M) to surface coating agent (Q) to 1:2.1:0.2.1:O (that is, no surface coating). did.

The surface coating was performed using a sand grinder (1/8G simple sand grinder, BSGI/8 (manufactured by Igarashi Kikai Co., Ltd.), and the grinding conditions were 2000 rpm.
I did it for 5 minutes.

To measure dispersibility, add each sample above to an aqueous solution,
The results are shown in FIG. 1 using 50% of the measured value by a laser particle size distribution analyzer (manufactured by Shimadzu Corporation).

From the results shown in this figure, the sample with the surface coating (M:Q=1:0.2) showed a dispersibility that was more than twice as high as that of the sample without the surface coating.

Magnetic powder containing Go-Fe203 in L belly and stem dispersibility test 1
(Particle size OJ ~ 0.4 μff1) Surface-coated magnetic powder was prepared in the same manner, and its dispersibility in an aqueous solution was tested. Compared to a sample without surface coating, It showed more than twice the dispersibility.

Example 1 6n powder (Go-containing-e20.: particle size 0.3~
0.4 μn+, coercive force Hc; 6590e, BET
(m”/g); 31.9° bulk density fg/In): 0
．． 70. Fe(X); 3.5”) 12.5g.

Coating agent polyoxyethylene allyl methyl diether (molecular weight 1524) and maleic anhydride alternating copolymer (repeat unit a) 1:25 g, and aqueous binder liquid (acrylic resin + water; blending ratio 40:60 wt)
96) Transfer 100 g to a cell (approximately 400 cc) for the sand grinder (described above), add the coating agent, binder liquid, and glass beads for stirring (particle size approximately 1.5 m + m) 20
Fill the powder with 155g of powder and 622g of powder in that order, insert a grinding blade into it, and then add 155g of powder from above.
glass pieces were added and stirred at 2000 rpm for 15 minutes. After stirring, the glass beads were removed to obtain about 10 g of a water-based paint containing magnetic powder.

This water-based paint containing magnetic powder was applied to one side of a polyester film (thickness 12 μm) for magnetic tape using a knife coater type coating machine (manufactured by Yasui Kinuki Co., Ltd.), and the width between the knife and the base was 1.
A magnetic recording medium using a water-based paint was obtained by applying the coating at a thickness of 5 μι, passing it through a magnetic field of about 3200 G to orient the particles, and drying with hot air (about 50° C.) to form a magnetic layer. The thickness of the obtained magnetic layer was about 110 At when applied wet and about 3 to 5 μm when dry.

The surface of the obtained magnetic recording medium was glossy, and there was no peeling when scratched with a fingernail, indicating high adhesion.

In addition, as a result of magnetic measurement using a vibrating sample type magnetometer BHV-55 (manufactured by Uken Denshi), the squareness ratio was 0.906 as shown in Figure 2 (the closer the squareness ratio is to 1, the more magnetic particles are on the film surface). It was confirmed that the coercive force was extremely high, 8200e (indicating that the magnets were arranged uniformly and with high density), and was found to be very suitable for industrialization.

Example 2 2.5 g of the surface coating agent of Example 1, 50 mJ of water
2 and 20 g of glass peas were filled into a sand grinder cell, then a blade was inserted, 25 g of magnetic powder and 155 g of glass peas were added, and the mixture was heated at 200 rpm.
After stirring for 5 minutes, spread it widely in a vat and add about 40 to 40 minutes.
It was dried at 5° C. for a day and night to obtain surface-coated magnetic powder.

Next, 13.75g of this surface-coated magnetic powder,
Water-based binder liquid (acrylic resin + water; blending ratio is 40
: 60 wt%i) 100 g was filled into a cell, a blade was inserted, 175 g of glass beads were added, and the temperature was heated to 200 O.
A magnetic powder-containing water-based paint was prepared by stirring at rpm for 15 minutes.

When this water-based paint containing magnetic powder was applied in the same manner as in Example 1 and its properties were measured, substantially the same results as in Example 1 were obtained.

Example 3 A magnetic recording medium was produced in the same manner as in Example 2, except that ethyl alcohol 50IIIL was used instead of water 50a+J2 in Example 2, and substantially the same results as in Example 1 were obtained.

Further, in this example, compared to Example 2, drying is easier and the drying time for obtaining a magnetic recording medium is shortened.

Example 4 Instead of the water-based binder liquid in Example 1, a water-based binder (acrylic resin dehydrate + ethyl alcohol; acrylic resin: water: ethyl alcohol - 40: 30: 3) was used.
0wt! A magnetic recording medium was produced in the same manner as in Example 1 except that Example 1 was used, and substantially the same results as in Example 1 were obtained.

In this example, compared to Example 1, magnetic powder was applied and
Drying after orientation was easy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the results of measuring the particle size distribution of the surface-coated magnetic powder of the present invention, and FIG. 2 is a diagram showing the results of measuring the squareness ratio of the magnetic recording medium produced in Example 1. . 4 others

Claims (1)

[Scope of Claims] 1. A magnetic powder-containing water-based paint containing dispersed magnetic powder whose main components are acrylic resin and water and whose surface is coated with an alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride, A magnetic recording medium characterized by having a coated magnetic layer formed by coating and drying on the surface of a substrate. 2. A magnetic powder-containing water-based paint is prepared by adding magnetic powder whose surface is coated with an alternating copolymer of polyoxyethylene allyl methyl diether and maleic anhydride to a binder liquid mainly composed of ethanol, acrylic resin, and water. , a method for manufacturing a magnetic recording medium, which comprises applying this water-based paint to the surface of a substrate and then drying it.