JPH0444632A - magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium which has good adhesive strength and decreases drop-outs by using a specific carbon black in a back coat layer and compounding a prescribed amt. of ammonium sulfate. CONSTITUTION:The back coat layer is formed to contain the carbon black having 6.0 to 12.0 pH and ammonium sulfate and the compounding ratio of the ammonia sulfate is specified to 0.5 to 5.0pts.wt. per 100pts.wt. compounding ratio of the carbon black. The adhesive strength of the back coat layer to a nonmagnetic material degrades if the pH is below 6.0. The reaction in a coating compd. is too fast and the thickening and gelatinizing are resulted when a hardener is compounded if the pH exceeds 12. The desired surface roughness of the back coat layer is then not obtainable. The effect of decreasing the drop-outs is lost if the compounding ratio of the ammonia sulfate is below 0.5pt.wt. per 100pts.wt. carbon black. The coating material thickens and the dispersion is difficult if the compounding ratio exceeds 5.0pts.wt. The chipping at the time of traveling is obviated in this way and the excellent adhesiveness is obtd. In addition, the drop-outs are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a magnetic recording medium comprising a magnetic recording layer provided on one surface of a non-magnetic material and a back coat layer provided on the other surface. The present invention relates to a magnetic recording medium for video that has a back coat layer that is effective in improving running stability and reducing dropout.

Conventional technology In recent years, magnetic recording media have been widely used as information recording media in fields such as audio and video, but as density increases, finer magnetic powder is used to achieve high dispersion of paint. , the surface roughness of the magnetic recording layer was also becoming smaller. As a result, the running properties of magnetic recording media have become difficult, and a back coat layer is provided to achieve running stability. Conventionally, various compositions of resin binders, inorganic fillers, lubricants, etc., have been proposed for back coat layers, as shown in Japanese Patent Application Laid-open No. 62-231418. The slippage properties have been improved.

Problems to be Solved by the Invention Although such conventional back coat layers have improved running durability and scratch resistance, they have weak adhesion to non-magnetic materials (such as peeling during running, In addition, there has been a problem of frequent dropouts, and it has been strongly desired to reduce dropouts caused by the back coat layer.

The present invention is intended to solve these problems, and aims to provide a magnetic recording medium with less dropout.

Means for Solving the Problems In order to solve the problems, the present invention provides a magnetic recording medium in which a magnetic recording layer is formed on one surface of a non-magnetic material and a back coat layer is formed on the other surface. The back coat layer is a magnetic recording medium containing carbon black having a pH of 6.0 to 12.0 and ammonium sulfate, and further, the amount of ammonium sulfate is 0.5 parts by weight per 100 parts by weight of the carbon black. ~5. (1 part by weight of the magnetic recording medium. The pH of the carbon black of the present invention is
5. The reason why it is limited to fl~12.0 is that if the pH is less than 6.0, the adhesive force of the back coat layer to the non-magnetic material decreases,
Furthermore, if the pH exceeds 12, the reaction in the coating material will be too rapid when a curing agent is added, resulting in thickening and gelation, making it impossible to obtain the desired surface roughness of the back coat layer. Also,
The reason why ammonium sulfate is added is because it has been found to be effective in reducing dropout, and also improves adhesiveness. The oil absorption amount of the carbon black of the present invention is 50 co/
100 g to 70 cC/100 g is suitable; this is because if the oil absorption exceeds 70, it will be difficult to uniformly disperse the paint.
In addition, if the oil absorption amount is less than 50, the surface roughness of the back coat layer becomes thick, which roughens the magnetic surface when wound and adversely affects the electromagnetic conversion characteristics.However, basically, the oil absorption of carbon black The amount and average particle diameter should be selected in accordance with the electromagnetic conversion characteristics of the magnetic recording layer, and the surface roughness should also be determined, and is not limited to the above range.

The amount of carbon black to be blended is suitably 40 to 180 parts, but is not particularly limited. The amount of ammonium sulfate used in the present invention is 0.5 to 100 parts by weight of carbon black.
A range of 5.0 parts by weight is effective.

This is because if it is less than 0.5 parts by weight, it lacks the effect of reducing dropout, and if it exceeds 50 parts by weight, the paint thickens and becomes difficult to disperse.

The resin binder used in the back coat layer of the present invention is a curable resin, and a combination of polyurethane and nitrocellulose is preferable. Examples of the polyurethane include N-2301 and N-2304 manufactured by Nippon Polyurethane Kogyo Co., Ltd. It will be done. In addition, examples of nitrocellulose include Seltsuba BTHI/16' manufactured by Asahi Kasei Industries, Ltd.
Examples include 1/2'. Further, as the curing agent for these resins, isocyanate-based curing agents are preferable, such as Coronate L manufactured by Nippon Polyurethane Industries, Ltd., and the like.

In addition, in the present invention, the magnetic recording layer formed on the opposite side of the back coat layer has a BET value of 37 m/g and Hc6700e.
Using iron oxide magnetic powder dispersed in a resin binder,
The surface roughness of the magnetic recording layer is about 0.02 μm.

Function The present invention can provide a magnetic recording medium with good adhesive strength and less dropout by using a specific carbon black in the back coat layer of the magnetic recording medium and adding a predetermined amount of ammonium sulfate.

Example Examples of the present invention will be described below.

First, after uniformly dispersing the following composition using a sand mill, ball mill, attritor, etc. alone or in combination, the isocyanate compound (Coronet) L
) was mixed in an amount of 20 parts by weight based on the weight part of the resin binder IH in terms of solid content, and the mixture was filtered to prepare magnetic paints and back coat paints ① to ②.

(Magnetic paint) Magnetic powder (BET=37i/g, He6700c) -1
00 parts by weight carbon black...1
〃A l 20 i...3
〃Vinyl chloride-vinyl acetate copolymer...1011
Polyurethane °°°9 Solvent (
MEK/)Luene/Nclohexanone・3/2/1)・
・・235 lt (back coat paint ■) Carbon black (pH 6,0 average particle size 23 mμ) -1H weight part C
OA/204 (spinel type composite oxide)...5 parts by weight Polyurethane...50" Nitrocellulose...50 Ammonium sulfate...0.5 Erosion J (VEX/)
Luene/cyclohexanone = 3/2/I)...150
0 Coronate L (solid content conversion)...2011 (
Back coat paint ■～■) The amount of ammonium sulfate added is 2 for back coat paint ■.
, 5 parts by weight, and 4.5 parts by weight for the back coat paint (■), except that the formulation was the same as that of the back coat paint (■).

(Back coat paint ■) Carbon black with pH 7.0 (average particle size 31 mμ)
The formulation was the same as back coat paint (■) except that .

[Comparative example]

The following comparative compositions were prepared in a manner similar to the above examples.

(Back coat paint ■) Carbon black with pH 2.5 (average particle size 23 mμ)
The formulation was the same as back coat paint (■) except that .

(Back coat paint ■) The formulation was the same as Nokutsu coat paint ■ except that ammonium sulfate was not added.

Examples 1 to 4 The magnetic paints of the above examples were applied to one side of a non-magnetic material made of polyethylene terephthalate, and a magnetic recording layer was formed by calendering, followed by the back coat paints shown in the above examples. (2) was applied to the other side and cured to form a back coat layer (0.6 μm) to obtain a magnetic recording medium.

Comparative Examples 1 to 2 Magnetic recording media were obtained in the same manner as in Examples 1 to 4, except that back coat paints 1 to 2 shown in the above Comparative Examples were used to form the back coat layer.

The test results of the magnetic recording media obtained in Examples and Comparative Examples are shown in the following table.

[Margin below]

As is clear from the results shown in the table above, in Examples 1 to 4, the back coat did not peel off during running, and it was found that not only did it have excellent adhesive strength, but it was also possible to provide a magnetic recording medium with fewer dropouts. did.

Note that the samples obtained in each Example and Comparative Example were tested by the methods shown below.

(1) Surface roughness: Rank Taylo+ Hobs
on Ta17s+ep surface roughness meter (LPF: 258
A length of 2 mm was measured using a 10-meter scale, and the value was divided into 10 equal parts, Rmax was determined in each section, and the average was taken.

(2) Video S/N: Matsushita Electric Industrial ■ VTR (NV
8200), and apply the specified luminance signal (50% white level signal) from the TV signal generator to the reference tape (Red-
2J), the signal-to-noise ratio (S/N) contained in the demodulated signal during playback was measured using a video color noise meter, and compared with that of the reference tape as OdB.

(3) t<ck coat ke fshi: VTR (NV 82
After running 200 times in an environment of 40° C. and 80% RH, the degree of scratches on the back coat surface was visually observed.

(4) Adhesion of back coat Under an environment of 20° C. and 60% RH, Sellotape was attached to the back coat layer of each sample and peeled off at 180°, and the load (g) at that time was taken as the adhesive strength. In addition, the number of samples for each sample is 10,
The average value was taken.

(5) Dropout = Record a single signal in an environment of 20°C and 60% RH, using a dropout counter,
Counts were taken per minute for 10 samples at 15 μs and 16 dB, and the average was taken.

Effects of the Invention As described above, according to the present invention, it is possible to provide a magnetic recording medium in which the backcoat layer is free from scratching during running, has excellent adhesive properties, and has little dropout, and is of great practical value.

Agent Hiroshi Mori Moto

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic recording layer formed on one surface of a non-magnetic material and a back coat layer formed on the other surface, wherein the back coat layer has a pH of 6.0. A magnetic recording medium characterized by containing carbon black of ~12.0 and ammonium sulfate. 2. The magnetic recording medium according to claim 1, wherein the amount of ammonium sulfate is 0.5 to 5.0 parts by weight per 100 parts by weight of the carbon black.