JPS5994230A - 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 a vinyl chloride - vinyl acetate copolymer to prepare a binder and by forming a coated magnetic film using the binder and magnetic powder. CONSTITUTION:Polyurethane resin and a vinyl chloride - vinyl acetate copolymer are used in 90:10-50:50 ratio. When the amount of the latter is increased in excess of the ratio, superior characteristics such as high sensitivity and a high S/N ratio are provided to the resulting recording medium, yet the magnetic layer is made rigid and has low durability. When the amount of the former is increased, the adhesive property is improved, yet the coefft. of friction is increased, and a magnetic 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 the polyurethane resin of this invention with <=20,000 number average mol.wt. and hydroxyl groups in the vinyl chloride - vinyl acetate copolymer, causing 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.

Structures of conventional examples and their problems In general, magnetic recording media are made by fixing magnetic powder with a binder to form a magnetic coating on a support such as poly or ester, and magnetic tapes, magnetic disks, etc. Are known. These magnetic recording media come into intense sliding contact with the magnetic head during recording and playback, which causes the magnetic layer to partially wear out and fall off, resulting in output fluctuations, drops, etc.
There is a problem in that the playback output may be output or the playback output may be decreased.

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

For example, vinyl chloride/viny 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. In addition, proposals have already been made to improve durability by mixing vinyl chloride/vinyl acetate copolymer or hydroxyl group-containing cellulose resin with high molecular weight polyurethane resin and acrylonitrile/butadiene copolymer, and adding incyanate. has been done. In addition, as a lubricant, higher fatty acids, fatty acid amides, esters, aliphatic hydrocarbons, silicone oils, etc. are used in the magnetic layer 3.
It has also been proposed to mix it into pages to improve durability.

However, in order to achieve durability of more than 100,000 busses 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, in a hot and humid environment, blooming may occur on the surface of the magnetic layer, or the magnetic layer may become soft and sticky.
This caused dirt on the magnetic head, causing problems with electromagnetic conversion characteristics and durability.

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 comprises a polyurethane resin having a number average molecular weight of 0.000 or less as a binder, and vinyl chloride.
The weight ratio of vinyl acetate copolymer is 90:10 to 60:
5o and has a number average molecular weight of 2,000
The desired purpose was achieved by using a material to which the following trifunctional low molecular weight incyanate was added, and by providing a magnetic coating film containing magnetic powder and the above-mentioned binder on a support. The magnetic recording medium of the invention will be explained in detail.

Conventional high molecular weight polyurethane resin with a number average molecular weight of 50,000 to 90,0008 degrees has a solid content of 36 degrees and 200 degrees.
The viscosity is relatively high at ~500 poise (25°C), whereas the low molecular weight polyurethane resin of the present invention with a number average molecular weight of 20,000 or less, for example 19,000, has a viscosity of 9 poise (26 °C) at a solid content of 35%. ℃) and relatively low viscosity.

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.

Page 5 However, in the present invention, if only the low molecular weight polyurethane resin is used and no trifunctional low molecular weight incyanate is added, the 100% modulus is as small as 22 Kg/cl, the mechanical strength of the magnetic layer is weak, and the durability is low. I have a sexual problem. 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 1 s -r Kg /l
ri and greatly improved. Conventional polyurethane resins [for example, N-2304 (number average molecular weight 50.000 to 70,000) manufactured by Nippon Polyurethane Industries Co., Ltd.] have a 100% modulus of about 17 Kg/cd1 when isocyanel is not added. Similarly to the above, even if 10 parts by weight of incyanate is added, the increase is only about 73 kg/lri. 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 past, and the magnetic head is free from dirt under both normal and high-temperature, high-humidity environments. Durability of 100,000 passes or more is achieved. A specific example of a commercially available polyurethane resin used in the present invention is NR-90 (number average molecular weight 19,000) manufactured by Nippon Polyurethane Industry Co., Ltd.

Further, in the present invention, the ratio of polyurethane resin to vinyl chloride/vinyl acetate copolymer is 90:10 to 6:
The reason for setting it to 50 is as follows. In other words, if the amount of vinyl chloride/vinyl acetate copolymer increases outside of this range, the dispersibility of the magnetic powder will improve and it will be possible to impart excellent electrical properties such as high sensitivity and high S/N ratio to the magnetic recording medium. , the magnetic layer becomes hard and scratches and wears due to sliding contact with the magnetic head, resulting in durability problems. Conversely, if the amount of polyurethane resin is increased beyond the scope of the present invention, the adhesion between the magnetic paint and the base film that is the support will improve, but the coating film of the magnetic layer will become soft and the coefficient of friction will increase. This causes dirt on the magnetic head.

In addition, the incyanate used in the present invention has trifunctional 7-page properties and a low molecular weight of 2oo○ or less. This trifunctional isocyanate has a number average molecular weight of 20.000 according to the present invention.
It reacts and crosslinks with the hydroxyl groups contained in the following polyurethane resins as well as vinyl chloride and vinyl acetate to form a tough film, significantly improving the abrasion resistance and heat resistance of the magnetic layer. The amount of trifunctional low molecular weight incyanate used in the present invention is usually 3 to 50% by weight based on the total amount of binder components.
The content is preferably 10 to 40% by weight. 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 the trifunctional low molecular weight incyanate compound include Coronate L manufactured by Nippon Polyurethane Industries, Ltd. and Desmodur L manufactured by Bayer.

As a magnetic powder that can be used in the present invention, conventionally known magnetic iron oxide powder (F e 304.
e 304 + 7 F e 203! Co-containing γ-Fe2o3, etc.).

Examples include chromium dioxide powder and metal magnetic powder.

Further, dispersants such as lecithin, antistatic agents such as carbon black JP-A-59-94230 (1), higher fatty acids, fatty acid amides.

Lubricants such as fatty acid esters, aliphatic hydrocarbons and silicone oils, Cr2o3. Abrasives such as At2o3 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: 100 parts Low molecular weight polyurethane resin: 24.6 parts (
NR-90, number average molecular weight 19000) Vinyl chloride copolymer...10.5 parts (U, C, C
, company product, VAGH) Carbon black ・River... 6 parts Dispersant ・River... 1 part Myristic acid ・・・・・・ 2 parts 9
Page silicone oil... river, 3 parts solvent (
MEK, ), luene) ... 180 parts (Comparative Example 1
) Co-containing magnetic iron oxide powder...100 parts High molecular weight polyurethane resin...24.5 parts (IIJ-
2304, number average molecular weight 5o, ooo~-ro, ooo
) Vinyl chloride copolymer...1o, 5 parts (U
, C, C0 company product, VAGH) 1-part dispersant for carbon blank
・River・1 part myristic acid
・Old...2 parts silicone oil
・・8 parts solvent (kJL E, K,
) Luene) ... 300 parts 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 incyanate (Corone L) manufactured by Nippon Polyurethane Industries Co., Ltd. 30 phr
After the addition, it was coated on a polyester film with a thickness of 75 μm and dried so that the film thickness after drying was 1.6 μm.

The surface of the magnetic paint layer was calendered with a 100 degree printing process, punched out into a disk shape, and the surface was polished to prepare a disk. We measured the durability of each sample and the dirt on the magnetic head.
The results shown in Table 1 were obtained.

(Margins below) Page 11 (Example 2) Co-containing magnetic iron oxide powder...100 parts Low molecular weight polyurethane resin...Part A (NR-
90, number average molecular weight 19,000) Vinyl chloride copolymer...Part B (U, C, C, company product, VAGH) Carbon black...6 parts Dispersant...・1 part lauric acid 2 parts silicone oil 3 parts solvent (y
LE, torxn) - 200 parts With the above paint composition, the total amount of binder A and B was 35 parts, and the composition ratios were varied as shown in Table 2 below. A magnetic disk was produced in the same manner as in Example 1 except for this.

The coefficient of friction, durability, and dirt on the magnetic head of each of the obtained samples were measured, and the results shown in Table 2 were obtained.

(Margins below Pages 13 and 14) The durability of each magnetic disk is determined by loading it into a recording/reproducing device under normal conditions (25℃, 60% Rf()) and under high temperature and humidity (50℃, ao% RH), pad pressure 15 (J
Continuous rotation was performed under the conditions of r, rotation speed of 30 Or, p, and 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.

The coefficient of friction in the table is determined by making sure that the magnetic layer side is in contact with a fixed post made of stainless steel with a diameter of 8 g++ over half the circumference, and applying an inlet tension of 50% to the fixed post.
gr, the tape running speed was set to 3.3o++/sec, the exit side tension was measured, and the friction coefficient (depression) 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. Cases are indicated by ○, cases where there is a small amount are indicated by Δ, and cases where there is a considerable amount are indicated by ×.

Effects of the Invention As is clear from the explanation on pages 15 and above, the present invention uses a polyurethane resin with a number average molecular weight of 20,000 or less as a binder and a vinyl chloride/vinyl acetate copolymer in a weight ratio of 9.
0:1o to 5o:50, to which a trifunctional low molecular weight incyanate was added, and a magnetic coating film containing magnetic powder and the binder was provided on a support. As a result, the magnetic head is free from dirt, the coefficient of friction against the contact surface with the magnetic head and pad is small, and it exhibits excellent durability even in hot and humid environments, making it suitable for practical use. The value above is great.

Name of agent: Patent attorney Toshio Nakao and 1 other person17
1-

Claims (1)

[Claims] As a binder, a polyurethane resin with a number average molecular weight of 20,000 or less and a vinyl chloride/vinyl acetate copolymer resin are contained in a weight ratio of 90:10 to 5o:50. 1. A magnetic recording medium, characterized in that a magnetic coating film containing a magnetic powder and the binder is provided on a support using a trifunctional isocyanate having a concentration of 2.000 or less.