JPS6318514A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a titled recording medium which has excellent electrical conductivity, light shieldability and durability and is suitable for high-density recording by providing an intermediate layer contg. a carbon black for which an urethane-modified nitrocellulose is used as a binder between a nonmagnetic base and magnetic layer. CONSTITUTION:The intermediate layer formed by incorporating the carbon black into the urethane-modified nitrocellulose is provided between the nonmagnetic base and the magnetic layer. The urethane-modified nitrocellulose is obtd. by bringing the urethane of a terminal isocyanate group and nitrocellulose into reaction. The amt. of the carbon black to be incorporated into the intermediate layer is 10-70wt%, more preferably 40-60wt% in terms of the electrical conductivity and light shieldability. The electrical conductivity is not enough if the amt. is <=10wt% and the voids of the intermediate layer increase and the surface smoothness is low if the amt. exceeds 70wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic recording tapes, 7O disks, and B-disks, and more particularly to magnetic recording media suitable for high-density recording.

[Conventional technology]

Many magnetic recording media have a magnetic layer on a non-magnetic support such as polyester, in which magnetic particles are dispersed in synthetic resin such as nitrocellulose. Carbon black was often contained in the magnetic layer. The reason for this is to prevent problems such as noise caused by charging of the magnetic recording medium and dropout caused by dust adhering to the magnetic layer, or to detect the end of a video tape or index hole of a floppy disk. This was done for the purpose of imparting light-shielding properties to magnetic recording media.

In recent years, there has been a trend toward higher density recording in 8A recording media, and attempts have been made to make the magnetic layer thinner in order to avoid loss in the thickness of the magnetic layer. This becomes a disadvantageous condition for the conductivity, light-shielding property, durability, etc. of the magnetic layer. In order to improve conductivity and light-shielding properties, it is possible to increase the amount of carbon black contained in the magnetic layer, but this reduces the ratio of magnetic particles in the acute layer, resulting in a decrease in reproduction output, and also increases the binder ratio. is also reduced, resulting in a decrease in durability.

In order to solve these problems, an intermediate layer containing carbon black and using a polyester resin as a binder is provided between the nonmagnetic support and the magnetic layer.

By this method - induction properties.

Although the problems of light-shielding properties and durability were solved, the surface smoothness of the intermediate layer deteriorated and the noise performance was poor, making it unsuitable for high-density recording. Therefore, the present inventors conducted intensive studies to improve the surface smoothness of the intermediate layer and found that the surface smoothness of the intermediate layer can be improved by using nitrocellulose as a binder. However, when nitrocellulose is used as a binder in this way, although the adhesive strength between the intermediate layer and the magnetic layer is sufficient, the adhesive strength between the non-magnetic support and the intermediate layer is low, resulting in poor durability. remained. To improve adhesive strength, Nitrocell 4-
However, in this case, the surface smoothness of the intermediate layer was poorer than that of cellulose alone, making it unsuitable for high-density recording.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a magnetic recording medium that eliminates the drawbacks of the conventional products described above, has excellent conductivity, light-shielding properties, and durability, and is suitable for high-density recording.

(Means for Solving the Problem) 1. As a result of intensive studies to achieve the above object, the present inventors found that the above object can be achieved by using urethane-modified p-su and internally plasticizing it. The inventors have discovered that this can be achieved, and have led to the present invention.

That is, in the present invention, between the nonmagnetic support and the magnetic layer,
An intermediate layer is provided containing carbon black using urethane-modified nitrocellulose as a binder.

The urethane-modified nitrocellulose used in the present invention is obtained by reacting urethane with terminal isocyanate groups and nitrocellulose.

For example, Tesla Tsuk υD, 1010 (polybutylene adipate manufactured by Hitachi Chemical Polymer Co., Ltd.) 6oy and 2-ptanone 2
Put 00f into 4 flasks of 11, heat and dissolve, then 6
While heating to 0'C and stirring, 10f of diphenylmethane diisocyanate and 0% of tin octylate were added in a 2% N flow.
．． 05y, a mixed solution of 50p of 2-butanone is added dropwise. After the addition was completed, the mixture was further stirred at 60″C for 2 hours, and then heated to 80°C.
The reaction was terminated by stirring at 100° C. for 2 hours. Then, 2-butanone was removed and drying was performed.

35 g of the above product, 2.5 g of l.6-hexamethylene diisocyanate, cyclohexanone/toluene (5 g)
0150) After dissolving 1509 in a 4-tube flask (No. 11), heat to 60"C and stir for 2 hours.

Next, after drying the modified nitrocellulose SS, 250f of cyclohexanone/toluene (50150) at 20w1t% was mixed and stirred at 30°C for 72 hours to obtain urethane-modified nitrocellulose.

As the binder for the intermediate layer, not only the above-mentioned urethane-based nitrocellulose but also polyisocyanate and/or polyurethane resin such as Coronet) L (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) may be added thereto. The amount of polyisocyanate added is preferably 50% or less, preferably 30% or less, based on the total binder. When it is more than 50%, the dispersibility of carbon black decreases, and the surface smoothness of the intermediate layer decreases. The amount of polyurethane resin added is
It is preferably 40 or less, preferably 20% or less, based on the total binder.

As the carbon black used for the intermediate layer, BET (
The specific surface area due to N2) is 10 to 300〆/f! DB
A material having an oil absorption amount of 40 to 200 cc/100 g due to P is suitable, and a material having the above-mentioned specific surface area of 25 to 260 I/I and an oil absorption amount of 50 to 180 squares/100 g is particularly preferred. An example of such carbon black is 5TERLING-1 (specific surface area 25g/f).

DBP oil absorption t7 lee/10J+, manufactured by Cabot, USA), 5TRRLING・NS (specific surface area 25g/f).

DBP oil absorption 70cc/7100y, manufactured by Cabot, USA), MOGυL (specific surface area 138g/f, DBP oil absorption fi 60cc/1007F, manufactured by Cabot, USA).

VULCAN-XC-72 (specific surface area 254ttf/
g, DBP oil absorption 178cc/100y, manufactured by Cabot, USA).

LAMPBLACKIOI C specific surface area 20g/p, D
BP oil absorption 65cc/loog, made by Degussa, West Germany), GEST 5H (specific surface area 60go/y, DBP@oil ff11)
32cc/100y, manufactured by Tokai Carbon Co., Ltd.).

The amount of carbon black to be included in the intermediate layer is 10 to 79w6%, preferably 4% from the viewpoint of conductivity and light shielding properties.
0 to 59 wt% is preferable. Carbon black is 10wt%
If it is less than 7Qwt%, the conductivity will not be sufficient, and if it is more than 7Qwt%, the middle layer will have more vacancies on the right side, and the surface smoothness will deteriorate.

Non-magnetic supports that can be used in the present invention include conventionally known polyethylene tetraphthalate, polyethylene-2
・Polyesters such as 6-7 talate, boroolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate and cellulose acetate p-bionate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, and polymers. Examples include plastics such as carbonate, polyamide, and polyimide, non-magnetic metals such as aluminum or alloys, paper, and paper laminated with polyethylene, etc., depending on the purpose.

〔Example〕

The details of the present invention will be explained below with reference to Examples.

Example 1 A paint for the intermediate layer was prepared as follows.

Carbon black (manufactured by Cabot, USA, MOGUL-
L): 100 parts urethane modified Nitrose/%/4-se: 80 r Schifta hexanone = 210 parts Toluene = 210 1 After mixing the above composition in a ball mill for 48 hours, Coronate L (Japan 20 parts by weight (n parts by weight) of Polyisocyanate (manufactured by Polyurethane Co., Ltd.) were added, and the mixture was further mixed and dispersed for 30 minutes to obtain a paint for an intermediate layer.

Apply the above paint to a polyester film (thickness - J 75μ)
An intermediate layer was formed by coating the surface so that the vJ dry thickness was 1 μm. The film and surface were also coated in the same manner.

Next, a magnetic paint was prepared as follows.

Co-containing 1-Fe2O3 powder = 100 am
Polyvinyl alcohol copolymer: 68 l Polyurethane: 41 l Oleyl oleate: 15 #Alumina = 1 o r toluene
:287# cyclohexanone
: 287# hardening agent (manufactured by Nippon Polyurethane Co., Ltd., Fronay L); 27 parts by weight of a magnetic paint was applied onto the polyester film coated with the above intermediate layer so that the dry film thickness was 1 μm, and the magnetic layer was After forming on both the front and back surfaces, surface smoothing treatment was performed. This sheet was punched out into a circular shape to obtain a F'O-)B disk.

Example 2 In the intermediate layer paint of Example 1, the amount of urethane-modified nitrocellulose was changed from 80 parts by weight to 50 parts by weight, and polyurethane (T-52 manufactured by Dainippon Ink and Chemicals) was added.
A floppy disk was obtained in the same manner as in Example 1, except that 30 parts by weight of 50") was added.

Comparative Example 1 In the intermediate layer paint of Example 1, polyester (Vylon 5 manufactured by Toyo U Co., Ltd.) was used instead of urethane-modified nitrocellulose.
30) A floppy disk was obtained in the same manner as in Example 1 except that the amount was changed to 80 parts by weight.

Comparative Example 2 In Example 2, urethane-modified nitrocellulose so NU! of the intermediate layer paint was used. Fl2) Rosel'y o -
A 7-P disk was obtained in the same manner as in Example 2, except that the amount was changed to 150 parts by weight. Comparative Example 3 In Example 1, the magnetic paint was applied directly onto the polyester film without applying the intermediate layer. Example 1
I obtained a floppy disk in the same way.

〔Effect of the invention〕

For the floppy disks obtained in Examples and Comparative Examples, the number of continuous actual runs until the light transmittance, resistance, modulation noise, and reproduction output became 70% or less of the initial output, that is, the durability was examined. The results are shown in the table.

As is clear from the above results, the present invention achieves light transmission by forming an intermediate layer containing carbon black between the nonmagnetic support and the magnetic layer using urethane-modified nitrosilane as a binder. rate, electrical resistance, modulation noise,
A magnetic recording medium that is excellent in all aspects of durability can be obtained.

Claims (1)

[Claims] A magnetic recording medium characterized in that an intermediate layer made of urethane-modified nitrocellulose containing carbon black is provided between a nonmagnetic support and a magnetic layer.