JPS61139930A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the bulk density of magnetic powder to improve the packability and to improve a magnetic characteristic by subjecting the magnetic powder pulverized by jet air flow to a surface coating treatment by a water soluble high polymer surface active agent. CONSTITUTION:The magnetic powder to be used as a magnetic recording element is brought into collision against each other in the jet air flow by which the powder is pulverized to the uniform pulverous powder. Such powder is subjected to the surface coating treatment by the water soluble high polymer surface active agent. The magnetic paint prepd. by mixing and dispersing such magnetic powder and binder is coated on a film and is dried, by which the recording medium having the magnetic layer is completed. The bulk density of the magnetic powder is therefore large and the packability in the stage of preparing the paint is good so that the smaller amt. of the org. solvent to be used is required. The magnetic density of the formed magnetic layer is high and the dispersion condition is good. The magnetic characteristic is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic disks.

C. Prior Art] Generally used magnetic recording media are made by coating a base made of polyester film or the like with a magnetic paint containing a binder and magnetic powder made of acicular particles, which are magnetic recording elements, and drying it. The magnetic layer is formed using the same method. Incidentally, the magnetic powder used in such magnetic recording media usually contains a high proportion of agglomerates due to various factors in the manufacturing process. For this reason, in the preparation stage of the magnetic paint, strong shearing force and impact force are applied using a kneader, ball mill, vibrating mill, etc. to loosen the agglomerates of the magnetic powder (unspecified literature).

However, with the above-mentioned means, there is a problem that shape destruction of the crystal grains progresses in parallel with the disappearance of the a agglomerates, leading to a decrease in the orientation of the magnetic powder and deterioration of the magnetic properties. There is also known a method of compressing and pulverizing agglomerates of magnetic powder on rollers, but this method is undesirable because the same problems as described above become more pronounced.

On the other hand, in recent years, the jet pulverization method, which uses the fluid energy of a jet stream to pulverize, is also being applied to magnetic powder (unspecified literature). According to this type of injection pulverization method, the agglomerates of magnetic powder are loosened without destroying the shape of the crystal particles, and it is expected that the excellent effect of improving the shape of the particles and narrowing the width of the particle size distribution will be expected. can.

[Problems to be Solved by the Invention] However, the magnetic powder that has been pulverized using the jet stream described above usually has a bulk density of 0 due to air entrainment.
Since the particle size is about 41 to 0.3 y/crn, it has poor filling properties when made into a paint (a large amount of solvent is required, which leads to a decrease in the magnetic properties of the magnetic recording medium due to a decrease in the density of the magnetic powder in the magnetic layer formed). There was a problem.

Therefore, an object of the present invention is to provide a magnetic recording medium with excellent magnetic properties by increasing the bulk density of the magnetic powder that has undergone jet pulverization using the jet stream and improving the packing property. There is.

[Means to Solve Problem No. 1] As a result of intensive studies for the above purpose, the inventors provided a coating layer made of a water-soluble polymer on the surface of magnetic powder particles that had been pulverized by a jet stream. In this case, the bulk density is significantly increased and the packing property is improved, and at the same time, the dispersibility is also improved due to the action of the water-soluble polymer coating, and the magnetic properties of the magnetic recording medium using the same are greatly improved. This discovery led to this invention.

That is, the present invention provides a method for manufacturing a magnetic recording medium in which a magnetic paint containing magnetic powder and a binder is coated on a base and dried to form a magnetic layer. The present invention relates to a method for producing a magnetic recording medium, characterized in that a magnetic recording medium whose surface has been coated with a water-soluble polymeric surfactant is mainly used.

[Structure and operation of the invention] In the method of this invention, magnetic powder used as a magnetic recording element is pulverized in advance with a jet stream. In this pulverization process, the powder is suspended in an air stream and moved at high speed, causing the powder particles to collide with each other in the process, resulting in a pulverizing action. The agglomerates that were present in a high proportion in the process are decomposed into individual crystal grains, and as mentioned above, there is almost no destruction of the particle shape, resulting in a uniform fine powder with a very narrow particle size distribution. .

In general, a circulating circuit type injection crusher that circulates the crushed powder at high speed in a suspended state is suitably used for such a crushing process using a jet stream, such as a jet-o-mizer mill or a micro jet mill. Preferably used. As for the pulverization processing conditions, it is usually preferable that the processing speed of the magnetic powder is 3 to 10 kg/hour and the jet stream pressure is about 2 to 7 KFllcrd.

In addition, in this invention, by using a classifier such as a cyclone together with the above-mentioned injection pulverizer, it is possible to remove coarse particles from the magnetic powder after pulverization and to obtain only particles in a narrower particle size range. be.

In the case of normal pulverization using air as a conveying medium, the magnetic powder to be subjected to the pulverization treatment using a jet stream as described above is T-Fe203, Fe3O4, an intermediate oxide of the former two, CO-containing T-Fe203, Co-containing Fe50. ．． .

Oxide magnetic powders such as CrO2 and barium ferrite are preferably used. However, by using an inert gas such as nitrogen gas or carbon dioxide gas, or a reducing gas such as hydrogen gas as a carrier medium, the above pulverization process can also be applied to metal magnetic powders such as Fe, Co, Ni, and their alloys. It is possible.

A feature of the present invention is that the surface of the magnetic powder that has been pulverized by the jet stream is coated with a water-soluble polymeric surfactant before being blended into the magnetic paint. In other words, the magnetic powder after the above-mentioned pulverization process entrains gas during pulverization and becomes a bulky fine powder with a bulk density of usually about 0.1 to 0.3 y/am3, so it has poor filling properties and is difficult to disperse when made into a paint. However, the above surface coating treatment significantly increases the bulk density, usually 0.7y/- or more, and improves the filling property, and the water-soluble polymer coating formed on the particle surface also improves the dispersibility in the magnetic paint. Greatly improved.

The water-soluble polymer surfactant used for this surface coating treatment usually has an average molecular weight of 1,000 to ioo, ooo.
It is preferable that the Also, as a representative example of this,
polyvinyl alcohol, carboxymethyl cellulose,
Examples include sulfonated styrene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, methylcellulose, sodium polyacrylate, polyethylene oxide, and derivatives thereof.

To carry out the above-mentioned surface coating treatment, the magnetic powder after the pulverization treatment is added to an aqueous solution of a water-soluble polymeric surfactant, sufficiently stirred, and then filtered and dried. in this case,
The magnetic powder is preferably used in an amount of about 5 to 20 parts by weight per 100 parts by weight of the aqueous solution of the water-soluble polymeric surfactant.
In addition, the concentration of the water-soluble polymer surfactant in the aqueous solution is 0.0
Approximately 5 to 0.5% by weight is suitable. It should be noted that if the concentration is lower than 0.05% by weight, the above-mentioned effects will be insufficient, and if the concentration is higher than 0.05% by weight, no further effects can be expected, which is uneconomical and requires a long time for drying.

In this invention, a magnetic paint containing a binder and magnetic powder, which is mainly made of magnetic powder that has been pulverized by a jet stream and surface-coated with a water-soluble polymeric surfactant, as described above, is prepared, and this is constantly used. A magnetic recording medium is manufactured by coating the magnetic layer on a base such as a polyester film and drying it according to the method and drying it to form a magnetic layer, and subjecting it to calendering or the like as necessary.

In this case, since the agglomerates of the magnetic powder are eliminated by crushing with a jet stream, strong shearing force or impact force to loosen the agglomerates is not required when preparing the dispensable paint. Sand mills, pearl mills, etc. can be used in place of conventional general-purpose eta, hole mills, vibration mills, etc., and even when the above-mentioned conventional general-purpose ones are used, the mixing and dispersion time can be significantly shortened.

Examples of the binder include vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral, polyurethane, epoxy resins, 47'y7 net compounds, etc., and conventional binders for magnetic powder 1. Any of those known as can be used. Further, various additives such as a lubricant, a dispersant, an abrasive, an antistatic agent, and the like may be appropriately blended into the magnetic coating material as required.

The magnetic recording medium thus obtained has excellent magnetic properties due to the high magnetic powder density and good dispersion in the magnetic layer, and has good surface smoothness because the magnetic powder has a uniform particle size and is well dispersed as described above. shows high electromagnetic conversion characteristics.

[Effects of the Invention] According to the method for manufacturing a magnetic recording medium according to the present invention, magnetic powder that has been pulverized in advance with a jet stream and then surface-coated with a water-soluble surfactant is mainly used. Therefore, compared to the case of using magnetic powder that has undergone only the above-mentioned pulverization treatment, the bulk density of the magnetic powder is increased, and when it is made into a paint, it has good filling properties, the amount of organic solvent used can be reduced, and its dispersibility is improved. . Therefore, the density of the magnetic powder in the formed magnetic layer is high and the dispersion state thereof is also good, resulting in a magnetic recording medium having excellent magnetic properties.

In addition, because the magnetic powder does not contain agglomerates and has a uniform particle size, and is well dispersed as described above, the surface smoothness of the formed magnetic layer is good, and the electromagnetic conversion characteristics of the resulting magnetic recording medium are also improved. be done.

〔Example〕

Next, the present invention will be specifically explained based on Examples and Comparative Examples. In addition, in the following, parts mean parts by weight.

Example 1 Using a micro jet mill (diameter 200 mm), Co-containing T-Fe20. Magnetic powder (specific surface area 30rrf/p, bulk density 0.55 y/(1)3, coercive force 62 oersted) was sprayed at an air injection pressure of 7 Kg/'7 and an air flow rate of 5 m3/
Pulverization treatment was carried out using a jet stream at a magnetic powder processing speed of 5 minutes and 9 parts time. Next, 10 parts of the above pulverized magnetic powder and 0.2 parts of sodium polyacrylate (average molecular weight 5,000) were added to 100 parts of water, thoroughly stirred, filtered, dried, and the particles Magnetic powder having a water-soluble polymer coating on the surface was obtained. Using the treated magnetic powder, a mixture having the composition shown below was mixed and dispersed in a sand mill for 1 hour to prepare a magnetic paint.

Cc-containing T-Fe, Q3 magnetic powder 100 parts Vinyl chloride-vinyl acetate-vinyl alcohol 18 parts Copolymer (product name VAGH manufactured by UCC) Polyurethane elastomer 12 parts (product name Bandex manufactured by Dainippon Ink Company) Trifunctionality Low molecular weight polyisocyanate compound 3 parts (trade name: Dismodulare, manufactured by Nippon Polyurethane Co., Ltd.) Lauric acid
2 parts cyclohexanone 80 parts
80 parts of this magnetic paint was then applied onto a base film made of polyethylene terephthalate with a thickness of 12 mm to a dry thickness of 41 nm, dried to form a magnetic layer, and then calendered to form a predetermined layer. A magnetic tape was produced by cutting it into widths.

Example 2 Sodium salt of sulfonated styrene-maleic acid copolymer (average molecular weight 5,
A magnetic tape was produced in the same manner as in Example except that 0.2 parts of the magnetic tape was used.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1, except that the pulverization treatment using a jet stream was not performed.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the surface coating treatment with sodium polyacrylate was not performed.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that neither the pulverization treatment using a jet stream nor the surface coating treatment using sodium polyacrylate were performed.

Comparative Example 4 A magnetic tape was produced in the same manner as Comparative Example 3, except that a ball mill was used instead of a sand mill to perform mixing and dispersion for 72 hours.

Various magnetic properties and surface smoothness were measured for the magnetic tapes obtained in the above Examples and Comparative Examples. The results are shown in the table below along with the bulk density of the magnetic powder before being mixed into the magnetic paint. The magnetic field used to measure the magnetic properties was IOK Oersted (Oe), and the surface smoothness was measured using a stylus-type surface roughness meter at a cut off of 0.08 m+++, and the center line average (CL A, ) was used to measure the magnetic properties. There is.

As is clear from the results in the above table, the magnetic tapes obtained by the method of this invention (Examples 1 and 2) have a large bulk density of the magnetic powder used, are highly filling, and are easily dispersible.
It has excellent magnetic properties such as residual magnetic flux density Br and squareness ratio B r /BS, and also has good surface smoothness.

On the other hand, in the case of the magnetic tape (Comparative Example 2) that was only subjected to pulverization treatment using a jet stream, a certain degree of surface smoothness could be obtained because the magnetic powder had a uniform particle size.
The bulk density of the magnetic powder is small and the filling and dispersibility are poor, resulting in greatly inferior magnetic properties. In addition, in a magnetic tape using magnetic powder that was not subjected to the above-mentioned pulverization treatment but only surface-coated with a polymeric surfactant (Comparative Example 1), the magnetic powder contained aggregated particles, so the magnetic properties were poor. In addition, even if the magnetic powder is easily dispersible, the surface smoothness is poor.

Furthermore, in a magnetic tape (Comparative Example 3) obtained using a sand mill that did not undergo the above-mentioned pulverization treatment and coating treatment and did not involve strong shearing force or impact force during the preparation of the magnetic coating material,
Since the magnetic powder contains aggregated particles and has low dispersibility, the magnetic properties and surface smoothness are significantly inferior.

On the other hand, in the magnetic tape obtained by the conventional general-purpose method of applying sufficient shearing force and impact force using a ball mill during the preparation of the magnetic paint (Comparative Example 4), the acicular shape of the magnetic powder particles is lost, so the method of the present invention The surface smoothness and magnetic properties are inferior to those made by As is well known, surface smoothness greatly affects electromagnetic conversion characteristics, and good surface smoothness improves sensitivity and S/N ratio.

Claims (1)

[Claims] (1) In a method for manufacturing a magnetic recording medium in which a magnetic paint containing magnetic powder and a binder is coated on a base and dried to form a magnetic layer, the magnetic powder is pulverized in advance by a jet stream and then highly water-soluble. A method for producing a magnetic recording medium, characterized in that a magnetic recording medium whose surface has been coated with a molecular surfactant is mainly used.