JPS59172117A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has the good surface smoothness of a magnetic layer, and has an excellent electromagnetic conversion characteristic, high modulus of elasticity and excellent mechanical strength by using a vinyl chloride/vinyl acetate copolymer contg. a specific amt. of a hydroxyl group, low-mol. wt. polyol and polyisocyanate compd. in combination as a binder component. CONSTITUTION:A vinyl chloride/vinyl acetate copolymer contg. >=6mol% hydroxyl group, low mol.wt. polyol and polyisocyanate compd. are incorporated as a binder component in a magnetic layer. The vinyl chloride/vinyl acetate copolymer contg. >=6mol% hydroxyl group contains much hydroxyl group and has good affinity to magnetic powder and therefore said copolymer can pack the magnetic powder at a high density by dispersing the same and contributes to an improvement in the dispersibility and packability of the magnetic powder. Acryl polyol, polyester polyol, etc. are examples for the low-mol.wt. polyol. The polyisocyanate compd. to be used in combination forms polyurethane by reactive curing with the polyol, and cross-links and bonds the vinyl copolymer by reacting with the OH group contained therein as well, thus improving modulus of elasticity and mechanical strength.

Description

Detailed Description of the Invention The present invention relates to a magnetic recording medium, and its object is to provide a magnetic recording medium with a magnetic layer having good surface smoothness, excellent electromagnetic conversion characteristics, high elastic modulus, and excellent mechanical strength. The goal is to provide a medium.

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating. The binder component used in this case has excellent dispersibility and filling properties of the magnetic powder, improves the smoothness of the surface of the magnetic layer, and can impart excellent electromagnetic conversion characteristics such as high sensitivity to the magnetic recording medium. It is necessary to choose a material that has excellent durability, high elasticity, and excellent mechanical strength, especially for magnetic tapes, etc., which are becoming more dense and thinner in recent years.
It is desirable to use a binder component that can sufficiently improve the surface smoothness of the magnetic layer, as well as provide high elasticity and good mechanical strength.

For this reason, various research and developments have been conducted on binder resins.
A vinyl chloride-vinyl acetate copolymer □ containing 6IIIO1% or more of hydroxyl groups has been proposed as having excellent dispersibility and filling properties of magnetic powder.

However, although this type of vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of hydroxyl groups has excellent dispersibility and filling properties of the magnetic powder, it is not able to sufficiently improve the surface smoothness of the magnetic layer. Another drawback is that the elastic modulus of the magnetic layer cannot be sufficiently improved.

The inventors conducted various studies in view of the current situation, and found that a vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of hydroxyl groups, a low molecular weight polyol, and a polyisocyanate compound were used as binder components for the magnetic layer. When used in combination, the dispersibility and filling properties of the magnetic powder are good, the surface smoothness of the magnetic layer is further improved, and the elastic modulus of the magnetic layer is also improved, resulting in a magnetic recording medium with high elasticity and even better mechanical strength. They found that it can be obtained and came up with this invention.

The vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of hydroxyl groups used in this invention has a high content of hydroxyl groups and has good affinity with magnetic powder, and therefore can disperse the magnetic powder well. The magnetic powder can be packed with high density, and the dispersibility and filling properties of the magnetic powder are improved. Specific examples of vinyl chloride-vinyl acetate copolymers containing 611io1% or more of such hydroxyl groups include, for example,
Examples include SRESOK A-5 manufactured by Blockbuster Chemical Industry Co., Ltd. and Denka #LOH1 manufactured by Denki Kagaku Kogyo Co., Ltd.

Furthermore, the low molecular weight polyols used in this invention include acrylic polyols, polyester polyols, polyether polyols, etc., all of which have an average molecular weight within the range of 200 to 1500 and a hydroxyl value of 2.
The average molecular weight is preferably within the range of 00 to 800, and if the average molecular weight exceeds 500 or the hydroxyl value is less than 200, the elastic modulus of the magnetic layer decreases. Since the viscosity of the paint increases and the amount of organic solvent must be increased, the surface smoothness of the magnetic layer is impaired. Furthermore, if the average molecular weight is lower than 200 or the hydroxyl value is higher than 800, the solubility in organic solvents will deteriorate, which is not preferable, and it is more preferable that the average molecular weight is 400 or more and the hydroxyl value is 700 or less. Here, the hydroxyl value refers to the number of potassium hydroxides required to neutralize acetic acid bound to an acetylated product obtained from 1 g of a sample. Specific examples of such low molecular weight polyols include Olestar Q-161 (acrylic polyol) manufactured by Mitsui Toatsu Chemical Co., Ltd.
, Adeka New Ace YT-400 manufactured by Asahi Denka Co., Ltd., Desmohen 800 manufactured by Nippon Polyurethane Co., Ltd., Desmohen 22'O manufactured by Nippon Polyurethane Co., Ltd.
O (all polyester polyols), Sunnisox TF'-400 manufactured by Sanyo Chemical Co., Ltd., Sunnisx CP-3000
Examples include Sannisox FA-908 (all polyether polyols). The ratio of the low molecular weight polyol to the vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of hydroxyl groups is the weight ratio of the vinyl chloride-vinyl acetate copolymer to the low molecular weight polyol.
The ratio is preferably in the range of 0:80 to 80:20; if the amount of low molecular weight polyol used is too small, the elastic modulus of the magnetic layer will decrease, and if it is too large, the dispersibility and filling properties of the magnetic powder will deteriorate.

The polyisocyanate compounds used in combination in this invention are isocyanates having at least two isocyanate groups in the molecule and adducts thereof, which react and cure with the above polyol to produce polyurethane. In addition, in this type of polyisocyanate compound, the isocyanate group also reacts with the OH group contained in the vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of the above-mentioned hydroxyl groups to form a strong crosslinking bond, and these crosslinking bonds cause magnetic properties. The elastic modulus of the layer is improved, a highly elastic magnetic layer is formed, the mechanical strength is further improved, and the surface smoothness of the magnetic layer is also improved. Specific examples of such polyisocyanate compounds include 1-methylpenzole-2,1
,6-) diisocyanate, triphenylmethane-4,
4',4''-triisocyanate, trimethylolpropane tolylene diisocyanate, etc. Specific examples of commercially available products include Coronate L manufactured by Nippon Polyurethane Industries, Desmodur Shi-75 manufactured by Bayer,
Desmodur L1 Type: Takenate D10 manufactured by Nichiyaku Kogyo Co., Ltd.
2 etc. The amount used is 1 for the total amount of binder components.
It is preferable to use it in a range of 0 to 50% by weight; if the amount is less than 10% by weight, the desired effect cannot be obtained, and if it exceeds 50% by weight, the crosslinking density becomes too high and the magnetic layer becomes hard and brittle. and results in a decrease in the surface treatment effect.

Examples of the magnetic powder used in this invention include r-F
e20B powder, Fe3O4 powder, Co-containing γ-Fe20
3 powder, Co-containing Fe3O4 powder, CrO2 powder and other F
Various conventionally known magnetic powders such as metal powders such as e-powder and CO powder are widely included.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, dimethylformamide, etc. are used alone or in combination of two or more.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, a magnetic powder, a vinyl chloride-vinyl acetate copolymer containing 6 mo1% or more of hydroxyl groups, and the like are placed on a substrate such as a polyester film. A magnetic paint containing a binder component consisting of a low molecular weight polyol and a polyisocyanate compound, an organic solvent, and other additives may be applied by any means such as spraying or roll coating, and dried.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 500 parts by weight S-LEC A-5 (vinyl chloride-vinyl acetate-vinyl alcohol copolymer manufactured by Sekisui Chemical 60μ Gyo Co., Ltd.) ADEKA New Ace YT-40011〃 (polyester polyol manufactured by Asahi Denka Co., Ltd., average Molecular weight: 400, hydroxyl value: 580) Desmodur L-75 (polyisocyanate compound manufactured by Bay 29 Engineering Co., Ltd.) Methyl isobutyl ketone 3501t Cyclohexanone 350〃Toluene
350 Put each component of the above composition except Desmodur Shi-75 into a ball mill, mix and disperse for 48 hours, add Desmodur Shi-75, and then add 1
After mixing and dispersing for a period of time, the mixture was taken out and a magnetic paint was prepared.

This magnetic paint was applied onto a 15μ thick polyester film to a dry thickness of 5μ. After being oriented in a DC magnetic field of 3000 oersted, it was heated and dried, surface treated, and then cut to a predetermined width to make a videotape.

Example 2 In the composition of the magnetic paint in Example 1, 12 parts by weight of Sannisox TP-400 (polyether polyol manufactured by Sanyo Chemical Co., Ltd., average molecular weight 400, hydroxyl value 430) was added in place of 11 parts by weight of Adeka New Ace YT-400. A videotape was made in the same manner as in Example 1, except that the amount of desmodule-75 used was changed from 29 parts by weight to 28 parts by weight. Comparative Example 1 In the composition of the magnetic paint in Example 1. , 21 parts by weight of Nisoporan 3023 (polyester polyol manufactured by Nippon Polyurethane Co., Ltd., average molecular weight approximately 2600, hydroxyl value 170) was substituted for 11 parts by weight of Adeka New Ace YT-400.
Use parts by weight and desmodule -75 to 29
A videotape was made in the same manner as in Example 1 except that the weight part was changed to 19 weight parts.

Comparative Example 2 In the composition of the magnetic paint in Example 1, Crisbon 4070 (urethane prepolymer manufactured by Dainippon Ink Co., Ltd.) was used in place of ADEKA NEW ACE YT-400, 11 parts by weight.
Example 1 except that 30 parts by weight of was used and the amount of desmodulated -75 was changed from 29 parts by weight to 10 parts by weight.
I made a videotape in the same way.

The surface smoothness, elastic modulus, and sensitivity (output of 5 Mllz) of the magnetic layer of each videotape obtained in each Example and Comparative Example were investigated using the following methods, and the results were as shown in the table below. . The ratio of polyol to polyisocyanate compound used in each of the Examples and Comparative Examples was adjusted so that the ratio of hydroxyl group to isocyanate group was 1.0 (equivalent).

Surface smoothness> Using a stylus type roughness meter, the surface average roughness 11 (C, L, A) of the magnetic layer was measured at a stylus speed of 0.06 cm/sec and a cutoff of 0.08 n. The quality of the surface smoothness was determined based on a relative value calculated according to the following formula using Example 1 as a reference.

<Elastic modulus of the example> The elastic modulus of the entire tape was measured under the conditions of a sample length of 10 cm and a tensile speed of 20/min, while the elastic modulus of only the polyester base film was measured, and the magnetic Find the elastic modulus of only the layer.

(dM + dB ) ET - dB EB Elastic modulus of magnetic layer = dM dM ; Thickness of magnetic layer can) dB : Thickness of polyester base film cm) E
T: Elastic modulus of the entire tape EB: Elastic modulus of the polyester base film From the elastic modulus of the magnetic layer of each sample calculated from the above formula, Example 1
A relative value was determined according to the following formula using the reference value as a reference, and it was determined whether the elastic modulus of the magnetic layer was large based on this relative value.

<Sensitivity> The 5 MHz output (dB) of each sample was determined using the example 1 as a reference (OdB).

3 As is clear from the above table, the videotapes obtained in Examples 1 and 2 had better surface smoothness, higher elastic modulus, and higher sensitivity than those obtained in Comparative Examples 1 and 2. This shows that the magnetic recording medium obtained by the present invention has excellent surface smoothness, high elasticity, and good sensitivity characteristics.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a vinyl chloride-vinyl acetate copolymer containing 5 mo1% or more of hydroxyl groups, a low molecular weight polyol, and a polyisocyanate compound as binder components.