JPS5994229A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having a low coefft. of friction and high durability and keeping a head clean by adding trifunctional isocyanate to polyurethane resin and an acrylonitrile-butadiene copolymer to prepare a binder and by forming a coated magnetic film using the binder and magnetic powder. CONSTITUTION:Polyurethane resin and an acrylonitrile-butadiene copolymer are used in 95:5-75:25 ratio. When the amount of the latter is increased in excess of the ratio, it becomes difficult to disperse magnetic powder, and superior durability is not provided to the resulting recording medium. When the former is increased, the powder is easily dispersed, yet the coefft. of friction is increased, and a head is not kept clean. Trifunctional isocyanate with <=2,000 low mol.wt. is added to said resins to prepare a binder. The isocyanate reacts with hydroxyl groups contained in the polyurethane resin of this invention with <=20,000 number average mol.wt., forming a tough film by cross-linking, so the wear and heat resistances of the magnetic layer are improved. The amount of the isocyanate to be added is usually 3-50wt% of the total amount of the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks.

Conventional Structures and Problems Generally, magnetic recording media are made by fixing magnetic powder with a binder to form a magnetic coating on a support such as polyester, and are known as magnetic tapes, magnetic disks, etc. . Since these magnetic recording media come into intense sliding contact with the magnetic head during recording and reproduction, the magnetic layer may partially wear off and fall off, causing output fluctuations, dropouts, or a decrease in reproduction output. It has problems.

Therefore, in order to solve this durability problem,
Various studies have been conducted on the type of binder that binds the magnetic powder to the base and the lubricant contained in the magnetic layer.

For example, vinyl chloride/vinyl acetate copolymer is used as a binder, and low molecular weight dioctyl phthalate acts as a plasticizer.

Alternatively, a mixture of high molecular weight polyurethane resin is known. It is also possible to improve durability by mixing vinyl chloride/vinyl acetate copolymer or hydroxyl group-containing cellulose resin with high molecular weight polyurethane resin and acrylic nitrile/butadiene copolymer, and adding incyanate. Already proposed. It has also been proposed that lubricants such as higher fatty acids, fatty acid amides, esters, aliphatic hydrocarbons, and silicone oils be mixed into the magnetic layer to improve durability.
.

There is.

However, in order to achieve durability of more than 10 million passes by sliding the same track of a magnetic disk with a magnetic head or pad under normal circumstances, in addition to selecting the type of binder, it is necessary to Conventionally, an excessive amount of lubricant was mixed in, which had to rely on the lubricity effect. For this reason, especially in high temperature and high humidity environments, plumping may occur on the surface of the magnetic layer, and the magnetic layer may become soft and sticky, causing dirt on the magnetic head and impairing its electromagnetic conversion characteristics and durability. It was causing problems.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems, and to provide a magnetic recording medium that has a small coefficient of friction, is free from dirt on the magnetic head, and exhibits excellent durability even in high-temperature and high-humidity environments. It is in.

Structure of the Invention The magnetic recording medium of the present invention uses a polyurethane resin having a number average molecular weight of 20,000 or less as a binder and an acrylonitrile-butadiene copolymer in a weight ratio of 95:5 to 75.
: Contains at a ratio of 25% and has a number average molecular weight of 2%.
The desired purpose was achieved by using a trifunctional low molecular weight incyanate having a molecular weight of 1,000 or less and providing a magnetic coating film containing a magnetic powder and the binder on a support.

The magnetic recording medium of the present invention will be explained in detail below.

Conventional high molecular weight polyurethane resins with a number average molecular weight of about 50,000 to 90,000 have a solid content of 36 inches and a
O~6. In contrast to the relatively high viscosity of ooo poise (25°C), the number average molecular weight of the present invention is 20.000 or less,
For example, a low molecular weight polyurethane resin of 19,000
It has a solid content of 35 cm and a relatively low viscosity of 9 poise (25°C). Therefore, if the low molecular weight polyurethane resin of the present invention is used, compared to conventional high molecular weight polyurethane resins, the amount of solvent in the paint can be reduced and the solid content can be increased.

However, in the present invention, the low molecular weight polyurethane 5'
-/If only the urethane resin is used and no trifunctional low molecular weight incyanate is added, the 100% modulus is as small as 221, the mechanical strength of the magnetic layer is weak, and there is a problem in durability. In the present invention, a trifunctional low molecular weight incyanate is added to the binder. For example, by adding 10 parts by weight, the 100% modulus is greatly improved to 1671. Conventional polyurethane resins [for example, N-2304 (number average molecular weight 50,000
~To, 000)), when no inocyanate is added, the 100% modinella is about 17η, but even if 10 parts by weight of isocyanate is added as above, the modinella is about 73η.
It only increases by about η. In view of this, it seems that the crosslinking density of the low molecular weight polyurethane resin of the present invention is significantly improved by the addition of the trifunctional low molecular weight incyanate, and a strong magnetic layer is formed.

As a result, the present invention eliminates the need to contain an excessive amount of lubricant in the magnetic layer as in the conventional case, and the magnetic head does not become contaminated under either normal or high-temperature and high-humidity conditions. Durability of 10 million passes or more is achieved. Specific examples of commercially available polyurethane resins used in the present invention include Nippon Polyurethane Industry Co., Ltd.
NR-90 (number average molecular weight 19.000).

Furthermore, in the present invention, the ratio of polyurethane resin to acrylonitrile-butadiene copolymer is 95=6 to 75:2.
The reason for setting it as 5 is as follows. That is, if the amount of the acrylonitrile-butadiene copolymer increases outside of this range, dispersibility with the magnetic powder becomes difficult, and the resulting magnetic coating film becomes flexible, causing problems in durability. Also,
On the other hand, if the amount of polyurethane resin is increased beyond the scope of the present invention, the dispersibility with the magnetic powder becomes easier, but the coefficient of friction increases, resulting in staining of the magnetic head.

Further, the isocyanate used in the present invention is trifunctional and has 2.
It has a low molecular weight of 000 or less. This trifunctional incyanate reacts and crosslinks with the hydroxyl groups contained in the polyurethane resin of the present invention with a number average molecular weight of 20,000 or less to form a tough film, improving the wear resistance of the magnetic layer to 7'/magnetism and heat resistance. significantly improves The amount of trifunctional low molecular weight isocyanate used in the present invention is usually 3 to 50 parts by weight, preferably 10 to 40 parts by weight, based on the total amount of the binder components. If this amount is too large, the coating film of the magnetic layer may become hard and brittle, while if it is too small, the desired effect may not be obtained. Specific examples of such trifunctional low molecular weight isocyanate compounds include:
Examples include Coronate L manufactured by Nippon Polyurethane Industries, Ltd. and Desmosil L manufactured by Bayer.

As magnetic powders that can be used in the present invention, conventionally known magnetic iron oxide powders (Fe304, Go-containing Fa30
4, r-Ee2o3. Go-containing r-Fe203, etc.).

Examples include chromium dioxide powder and metal magnetic powder.

In addition, dispersants such as lecithin, antistatic agents such as carbon black, higher fatty acids, fatty acids, fatty acid esters, aliphatic hydrocarbons, and lubricants such as silicone oil, 0r20, 1. Jj? Abrasives such as 203 are also used. As for the support for the magnetic coating, polyester, polyacetate, polyimide, or polyamide films are used.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be specifically described. It should be noted that all parts mentioned in the Examples mean parts by weight.

(Example 1) CO-containing magnetic iron oxide powder...Track 1oo part Low molecular weight polyurethane resin...24.
5 parts (NR-90, number average molecular weight 19,000) acrylonitrile-butadiene copolymer...1o,
5 parts (manufactured by Nippon Zeon ■, Nippor 1432J) carbon black, song, 6 parts dispersant
・・Song 1 part myristic acid
・・・・・・ 2 parts Silicone oil ・・・・・・ 3 parts Solvent (ME
(K,) luene)...180 parts (Comparative Example 1) GO-containing magnetic iron oxide powder: 100 parts High molecular weight polyurethane resin: 24.6 parts (
N-2304, number average molecular weight 50,000-70,00
0) Acrylo-nitrile-butadiene copolymer...
...10.5 parts (manufactured by Nippon Zeon ■, Nisopol 1432
J) Carbon blank...
・6-part dispersant・・・・・・
・1 part myristic acid ・・・・
・・2 parts silicone oil ・・・
... 8 parts Solvent (MEK, toluene) ...
SoO part The magnetic paints having the compositions of the above Examples and Comparative Examples were mixed in a ball mill for 48 hours, and trifunctional low molecular weight isocyanate (Nippon Polyurethane Industries ■) was mixed for 48 hours.
After adding 30Phr of Coronate L), the thickness was 7.
On a 5 μm polyester film, the film thickness after drying is 1
．． It was coated and dried to a thickness of 6 μm. Next, the surface of the magnetic paint layer was calendered, punched into a disk shape, and the surface was polished to produce a magnetic disk. When the durability of each sample obtained and the contamination of the magnetic head were measured, the results shown in Table 1 were obtained.

10.1.・Table 1 (Example 2) GO-containing magnetic iron oxide powder... 100 parts Low molecular weight polyurethane resin... Iribe (NR-90,
Number average molecular weight 19,000) Acrylo nitrile-butadiene copolymer... Part B (manufactured by Nippon Zeon ■, Nippor 1432J) Carbon black
Bright... 6-part dispersant ・
... 1 part lauric acid
・Song 2nd part silicone oil ・・
Song 3 parts Solvent (MKK, toluene)...
200 copies of music With the above paint composition, the total amount of binder A + B is 35 parts, and various composition ratios 1 as shown in Table 2 below.
A magnetic disk was produced in the same manner as in Example 1, except that the ratio was changed at a rate of 1-7. The coefficient of friction, durability, and contamination of the magnetic head of each of the obtained samples were measured, and the results shown in Table 2 were obtained.

(Part 1, Ding Zong Bai) 137-The durability of each magnetic disk was measured when it was loaded into a recording/reproducing device under normal environment (26℃, 60%RH) and under high temperature and humidity (50℃, 280%RH). RH), butt pressure 15gr
Continuous rotation was performed under the conditions of , rotation speed 30 Or, p, m, and the rotation speed is shown as the rotation speed until the reproduction output of the magnetic disk becomes 70% or less of the initial output.

In addition, the friction coefficient in the table is calculated by setting the magnetic layer side in contact with a fixed post made of stainless steel with a diameter of 8 ff over half its circumference, and applying tension on the entry side to the fixed post in s□g.
r, the tape running speed was set to 3.3 w/sec, the exit tension was measured, and the friction coefficient (→) was determined from the following equation.

Also, for reference in each table, in a magnetic disk durability test, the surface of the magnetic head was visually observed when the playback output decreased to 70% of the initial output, and the surface of the magnetic head was visually observed to find that there was almost no dirt visible. The case is indicated by ○, the case of a small amount is indicated by Δ, and the case of a considerable amount is indicated by X.

Effects of the Invention 14'' As is clear from the above description, the present invention uses a polyurethane resin with a number average molecular weight of 20,000 or less and an acrylonitrile-butadiene copolymer as a binder in a weight ratio of 95 = Contains in a ratio of 6 to 75:25, and 3
It uses a functional low-molecular-weight incyanate, and is constructed so that a magnetic coating film containing magnetic powder and the binder is provided on a support, so that it does not stain the magnetic head and does not damage the magnetic head, pads, etc. It has great practical value because it has a small coefficient of friction on contact surfaces and exhibits excellent durability even in high-temperature, high-humidity environments.

Claims (1)

[Scope of Claims] As a binder, a polyurethane resin having a number average molecular weight of 20,000 or less and an acrylonitrile-butadiene copolymer are contained in a weight ratio of 96=5 to 75:25; The molecular weight is 2. o o. A magnetic recording medium characterized in that a magnetic coating film containing a magnetic powder and the binder is provided on a support by adding the following trifunctional incyanate.