JPS58199437A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance traveling stability, by forming a magnetic layer on the front face of a nonmagnetic support and on the opposite side forming a back coat layer contg. fine particles including at least grainy ones of magnetite. CONSTITUTION:Fine magnetite particles of 0.01-0.5mum diameter are prepared by the coprecipitation method, the method of reduction of alpha-Fe2O3 or gamma-Fe2O3, or that of oxidation of iron powder. the magnatic layer may comprise any of magnetic iron oxide, chromium dioxide, and metallic magnetic powder. As abrasive added when needed, a high hardness fine powder, such as Cr2O3 or alumina, is used, and carbon black or graphite particles are used for an antistatic agent. An organic solvent, such as methyl ethyl ketone or toluene, is used. The back coat layer is formed before and after formation of the magnetic layer, or after calender treatment, or the like.

Description

[Detailed description of the invention] The present invention relates to a magnetic recording medium, and its running properties.

The purpose is to provide a magnetic recording medium with excellent durability.

Magnetic recording media include magnetic tape, magnetic tape, vI
There are K-ki cards, etc., which are used for audio, video, and computers, and have seen remarkable development in recent years.

Each of these recording media is increasingly suitable for high-density recording, and for this purpose, the recording wavelength is short, the recording track width is narrow, and the recording medium thickness is thin.Furthermore, the SIN ratio and sensitivity two-frequency characteristics are to be excellent. In addition, the surface properties of the two-page magnetic layer are becoming increasingly smooth. However, -deterioration increases the friction coefficient and reduces running performance.

This is disadvantageous in terms of durability.

For this reason, magnetic recording media aiming at high density recording, high S/N ratio, and high sensitivity are desired to have good magnetic surface properties, low coefficient of friction, and excellent wear resistance. As a result of intensive research on the above points, the present invention has been developed by providing a coating layer (back coat layer) containing granular magnetite particles on the opposite side of the magnetic layer via a non-magnetic support.
The present invention was made based on the discovery that a magnetic recording medium with less chargeability, a lower coefficient of friction, and excellent running stability can be obtained than before. Granular magnetite particles.

A composition consisting of a binder, a lubricant added as necessary, and a solvent is thoroughly mixed and dispersed to form a backing coating. The other side? By coating on a non-magnetic support and drying, in other words, by providing a magnetic layer on one side of the non-magnetic support and a back coat layer on the other side.
1, it provides a magnetic recording medium with extremely excellent running properties; ゛・゛ 1
...Magnetite fine particles are black and have low electrical resistance.
□.

Therefore, a magnetic recording medium provided with a back coat layer containing this material has less chargeability and lower light transmittance than a conventional magnetic recording medium without a coat layer. The coefficient of friction is lower than that of the polyester fiber containing the lume base.
For these reasons, it is believed that the magnetic recording medium of the present invention has much more stable running performance than a conventional magnetic recording medium without a back coat or layer.

The magnetite fine particles for the back coat used in the present invention may be made by any of the coprecipitation method, the reduction method from α-Feo3 or γ-Fe2O3, and the oxidation method of metal iron powder. The particle size of these magnetite fine particles is 0.
A size of 0.01 to 0.5 μm is preferred.

If the particle size is less than 0.01 μm, dispersion in the backcoat paint becomes difficult, and if it exceeds 0.5 μm, there is a problem that the surface of the backcoat layer becomes rough.

, - Next, a method for manufacturing a magnetic recording medium according to the present invention will be explained using magnetic deso as an example.

First, the magnetic layer is formed as follows.

Magnetic powders include magnetic iron oxide and chromium dioxide.

Any metal magnetic powder may be used. Abrasives added as needed include Cr2o3. Al2O3,, S z Ct
High hardness fine powders such as T 102 are available, and antistatic agents include powder, carbon black or graphite particles.

These inorganic pigments, the above-mentioned thermosetting mixture, higher fatty acid ester, higher fatty acid, lecithin, etc. are thoroughly mixed and dispersed together with a solvent in a mixer to prepare a magnetic coating liquid having a desired component ratio. .

The organic solvent used here can mainly be methyl ethyl ketone, toluene, methyl isobutyl ketone, cyclohexanone, ethyl acetate, etc. As a mixer, a ball mill is used.

You can use a sand mill, desilver, attritor, high speed mixer, kneader, etc.

5""-' Next, the magnetic coating liquid is coated onto a support such as a polyester film. As for the application method, doku1'-7”L
/-)” method: f5 No. A method '+7 /(-7'.

- Any method is acceptable. Immediately after application, contact and seal with □tlahshangr'L4 to ensure the smoothness of the coating film.

However, this includes Bar Smoother, Wire Smoother,
Any film smoother or the like may be used.

After the sheep is dried, a magnetic field distribution gate is used to align the magnetic powder in the coating film in one direction, and the urine is passed through a suitable magnetic field once, and the magnetic field strength is Although it varies depending on the coercive force of the powder, it is preferably about 2 to 4 times the coercive force.

Magnets include permanent magnets and electromagnets. After such orientation treatment, it is dried to remove the solvent.

In order to make the surface of the magnetic layer of the dried wide magnetic film even smoother, the surface of the dried wide magnetic film is treated with a 72° roll. At this time, the surface property of the magnetic field has a great influence on the magnetic transformation i property □ of the magnetic data. Calendar conditions are 6 pages, temperature 50-100℃, pressure 50-400K517cm
.

Next, a back coat layer is formed as follows.

A back coat material having a desired component ratio is prepared by mixing and dispersing the above magnetite fine particles, a binder, a lubricant added in a small amount if necessary, and the like using a solvent. The binder used in this case is a conventionally known thermoplastic resin,
Single or mixed systems such as thermosetting resins or reactive resins can be used. Junkan agents include high-grade fatty acid lubricants.

The back coat paint thus obtained is applied onto the support on the opposite side where the magnetic layer will be provided. The process up to drying is exactly the same as the method for forming the magnetic layer except for the "orientation treatment".

The timing to provide the hard layer is (1) before forming the magnetic coating film, (11) after forming the magnetic coating film, and (ii) after forming the magnetic coating film.
D: After the magnetic coating film is calendered, etc., 7 pages may be applied, but any time is fine.

As described above, a wide magnetic film (jumbo roll) with a magnetic surface treated and a back coat layer is shredded into a predetermined width. It is important to minimize width variation.

During the final product assembly process, it is important to prevent dust and other deposits from adhering to the tape surface, which may cause dropouts.

Hereinafter, the present invention will be specifically explained based on Examples. It should be noted that all parts in the component ratios described in the Examples indicate parts by weight.

(Example 1) A magnetic paint and a back coat paint were prepared as follows.

1. Preparation of magnetic material Co-containing -Fe2o3 magnetic iron oxide powder...10
0 parts for Yamakawa...15 parts (N-3113 manufactured by Nippon Polyurethane Co., Ltd.) Vinyl chloride-vinyl acetate copolymer...Bright...5 parts (VA manufactured by UCC Company)
GH) Nitrocellulose resin・・・・・・・・・：・・
... River ... 5 parts (RS 3A manufactured by Daicel) Chromium oxide (CT203) powder ......
... Mountain: 3 parts Lecithin ... Beating: ... 2 parts Methyl ethyl ketone (Mxx).
Yamakawa...10'O methyl isobutyl ketone (MIBK
) River: 100 parts Toluene Used: 100 parts After mixing and dispersing the above composition in a ball mill for 48 hours, e parts of Pardner (Coronate L) were added, and the resulting contaminant was mixed with an average pore size. A magnetic coating solution was prepared by filtering through a 3 μm filter.

2. Back coat paint magnetite (Fe3o4) powder ・River...River...
100 parts Average particle size = 0.1 μm Polyurethane resin ・Yamakawa 30
Part 9 Page (N-2304 manufactured by Nippon Polyurethane Co.) Vinyl chloride-vinyl acetate copolymer 20 parts (VAGH manufactured by UCC) Methyl ethyl ketone (MEK) 10
0 parts Methyl isobutyl ketone (MI BK)...1
00 parts toluene ・Used and used ・100
After mixing and dispersing the above composition in a ball mill for 24 hours,
A mixed substance obtained by adding 10 parts of hardener (Coronet L) was filtered through a filter having an average pore size of 3 μm to prepare a back coat paint.

Next, the above magnetic paint was applied onto a 16 μm thick polyester film, oriented and dried, and then the magnetic layer was surface treated using a super calender roll to obtain a wide jumbo roll with a magnetic layer of 6 μm thick. Using this jumbo roll, the pick coat paint was applied to the back surface opposite to the magnetic layer and dried to form a back coat layer having a coating thickness of O.mu.m. This was shredded into % inch width pieces to make a videotape (Example 2) Page 10 Using the same magnetic paint and back coat paint as in Example 1, first apply the back coat paint to a 16 μm thick film. It was applied onto a polyester film and dried.

Next, magnetic paint is applied to the back side, oriented, and dried.
The surface was processed using a super calender roll to obtain a wide jumbo roll having a magnetic thickness of 5 μm and a back coat layer thickness of 1 μm. This was cut into pieces of Z inch width to produce a videotape.

(Comparative Example χ A surface-treated jumbo roll having only a magnetic layer without a back coat layer was obtained in Example 1, and this was cut into pieces Z inches wide to produce a videotape. The following table shows the characteristics of each sample, such as charged potential, light transmittance, friction coefficient of the back surface opposite to the magnetic layer, and winding disorder state.

(Leaving space below) In the table above on page 11, (1) The charge potential is +6 on the sample using an electrostatic copying paper tester.
KV was determined from the maximum accepted potential when charged for 10 seconds.

(2) Light transmittance is calculated from the ratio of the total amount of light received when there is no tape to the amount of transmitted light when there is tape using the end sensor of the VH8 video tape recorder NV-8200 (manufactured by Matsushita Electric Industrial Co., Ltd.) I asked for it.

(3) The coefficient of friction is determined by making sure that the back side of the tape is in contact with an aluminum alloy drum with a diameter of 126 m+ over half its circumference.
Set the inlet tension on the drum to 35P1 and set the running speed to 3.
, 2 crr/sec, the exit side tension was measured, and the friction coefficient was determined from the following equation.

(4) Disturbances in winding were determined by visually checking the winding appearance after fast forwarding and rewinding.

As is clear from the table above, the magnetic tape obtained in the above manner has less electrostatic charge than conventional products, has a lower coefficient of friction, and has a lower light transmittance, resulting in extremely stable tape running. ing. In the above embodiment, a magnetic tape was explained, but the gist of the present invention is not only a magnetic tape but also a magnetic sheet.

Needless to say, it can be applied to magnetic recording media such as magnetic cards.

As described in detail above, according to the present invention, a magnetic recording medium with excellent running stability can be obtained, and therefore has great practical value.

Claims (1)

[Claims] A magnetic recording medium 0 comprising a magnetic layer provided on one main surface of a non-magnetic support, and a back coat layer containing at least granular magnetite fine particles provided on the other main surface of the non-magnetic support.