JPS595428A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a superior magnetic recording medium for use in a VTR, etc., enhanced in antistaticness, abrasion resistance, etc., and prevented from irregularly winding, by forming a backing layer contg. BaSO4 and carbon black both having specified particle diameter ranges on the side of the support reverse to the magnetic layer. CONSTITUTION:The backing layer formed on the side of the support reverse to the magnetic layer contains BaSO4 (Ba) having 0.2-2mum average particle diameter by 30-80wt% of the total of the (Ba) and the binder of the backing layer, and carbon black (CB) having <=0.1mum average particle diameter by 20-80wt% of the total of (Ba) and (CB) and other fillers added when necessary, and polyurethane, vinyl chloride-vinyl acetate polymer, or the like is used for the binder resin. As a result, the obtained magnetic tape is superior in antistaticness, resistance to irregular winding, and video characteristics, and free from danger of damaging a guide, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the back coat layer of a magnetic recording medium such as a video tape, which is formed by providing a back coat layer on the back surface of a base having a magnetic layer on its main surface.

For magnetic tapes used in reel-to-reel VTRs, a back coat layer in which carbon black and other appropriate fillers are dispersed and bound in a binder is applied to the back of a base having a magnetic layer on its main surface. This prevents the tape from being statically charged and from winding irregularly, and also improves the abrasion resistance of the back surface of the tape (prevents scratching of the back surface).

However, depending on the filler used in combination with carbon black, a sufficient effect of preventing winding disorder may not be obtained, or the abrasion resistance of the back surface of the tape may not be sufficiently improved. Another problem is that by providing this type of back coat layer, there is a fear that when the back coat layer comes into sliding contact with a VTR guide or the like, the sliding contact portions may be damaged.

As a result of intensive studies from the above point of view, the inventors found that the filler used in combination with carbon black has an average particle diameter of 0.
By using barium sulfate with a thickness of 2 to 2μ, it is possible to form a back coat layer that has excellent not only antistatic properties but also anti-winding and abrasion resistance.Moreover, this back coat layer has V
It was discovered that there is little risk of damaging the TR guide, etc., and this invention was made.

This effect of barium sulfate is due to the fact that this type of filler is well dispersed in various binders, has an appropriate Mohs hardness of about 3, and has an average particle size of 0.2 to 2μ. This is based on the fact that it is set within the range of . Here, when the average particle diameter is less than 0.2 μm, the surface roughness of the back coat layer will not be sufficient and the winding disorder property will deteriorate. On the other hand, if it exceeds 2μ, the surface condition becomes extremely poor, which affects the magnetic layer during tape winding, resulting in a significant loss of video characteristics, making it unsuitable as a back coat layer.

The content of barium sulfate is preferably such that it usually accounts for 30 to 80% by weight of the total amount of the backcoat layer together with the binder; if this amount is small, the above effects cannot be obtained, and if it is too large. This may damage the coating film properties and adversely affect the video properties.

The carbon black to be used in combination with barium sulfate should preferably have an average particle size of 0.1 μm or less, and may have particularly good dispersibility in binders such as Black Pearl L manufactured by Cabot, as well as MA manufactured by Mitsubishi Chemical Corporation.
General commercially available carbon blacks such as -600 can be widely used. The amount used is generally 20% of the total weight of the barium sulfate and other fillers that can be added as necessary.
It is preferable that the proportion be 80% by weight.

There are no particular restrictions on the binder for binding the above-mentioned barium sulfate and carbon black, and any binder with excellent adhesiveness to the base, abrasion resistance, etc. can be used.

Examples include cellulose resin, polyurethane resin, polyester resin, polyisocyanate, and vinyl chloride-vinyl acetate copolymer resin.

The back coat layer in this invention is formed by applying a coating material in which barium sulfate and carbon black are mixed and dispersed in the above-mentioned binder to a thickness of usually 13 to 5 μm on the back surface of a base on which a magnetic layer has been previously formed on the main surface. However, this layer may contain various additives such as a suitable lubricant as necessary.

The lubricant reduces the coefficient of friction of the backcoat layer to improve durability, and also provides good results in preventing filler powder from falling off. Any material that is solid (semi-solid) or liquid at room temperature can be used as long as it is soluble in organic solvents.

Specific examples include fatty acids, fatty acid esters, liquid paraffin, and the like. The amount added is preferably 5 parts by weight or less (usually 0.01 to 5 parts by weight) based on 100 parts by weight of the total filler.

As described above, according to the present invention, it is possible to provide a magnetic recording medium which has not only antistatic properties but also excellent anti-wound and abrasion resistance, and which is resistant to souffling and damage to VTR guides and the like.

Next, embodiments of this invention will be described. In the following, parts shall mean parts by weight.

Example CO-containing acicular magnetic iron oxide powder 250 parts carbon black 12 parts granular α-iron oxide 20 parts nitrified cotton
22 parts polyurethane resin
20 parts trifunctional low molecular weight isocyanate compound
8 parts cyclohequinosane 310 parts toluene 310 parts n-butyl stearate 3 parts liquid paraffin
2-part myristic acid
2 parts of magnetic paint having the above composition, 20 parts
It was coated onto a μ-thick polyester base film with good surface smoothness to a dry thickness of 6 μm, dried, and then subjected to surface treatment.

A back coat paint having the composition shown below is applied to the back of the obtained magnetic tape so that the dry thickness is 3.5 μm. After drying, surface treatment is performed, and the video tape is cut to a specified width. I made it.

Barium sulfate 180 parts Pearlized, volatile components 5% by weight Nitrified cotton 100 parts Polyurethane resin 70 parts Trifunctional low molecular weight incyanate compound 30 parts n-butyl stearate 3 parts Myristic acid
2 parts liquid paraffin
3 parts Cyclohexanone 750 parts Toluene 750 parts The surface electrical resistance, anti-winding properties, abrasion resistance, scratch resistance to guides, and video characteristics (color S/N ratio) of the back coat layer of the above video tape were evaluated using barium sulfate. The results of the investigation using the particle size as a parameter are shown in the table below.

In the table, Comparative Example 1 is the result of a videotape produced in the same manner as in the Example except that no backcoat layer is provided, and Comparative Examples 2 and 3 are the results of a videotape produced in the same manner as in the Example except that no backcoat layer is provided, and Comparative Examples 2 and 3 are the results of a videotape made in the same manner as in the Example except that no backcoat layer is provided. Comparative Example 4 is a videotape produced in the same manner as in Example except that titanium oxide with a particle size of 0.5μ was used instead of barium sulfate. This is the result. Moreover, each characteristic test was conducted by the following method.

<Surface specific electrical resistance> Two rod-shaped metal electrodes each having a cross section of a quarter circle with a radius of approximately 1a are placed 25.4 mR apart, and a sample is placed on top of these electrodes at right angles to each other. Hang a 300y weight. In this state, an arbitrary DC voltage of 500 μ was applied between both electrodes, the current was measured, and the resistance value was calculated.

<Anti-winding property> 25.4 m wound 1410 m on a 26 type 96 minute reel
m width sample tape was transferred to a 1 inch helical VTR (type C
), the tape was fast-forwarded and rewound at high speed over the entire length of the tape, and then the appearance of the tape rewound onto the reel was observed and evaluated.

<Abrasion resistance> After loading a 25.4mm wide sample tape wound on a reel into a 1-inch helical VTR (type C) and running the test repeatedly 500 times, the number of scratches that occurred on the back of the tape was determined. The abrasion resistance was evaluated based on the amount.

<Scratch resistance> After replacing one of the guide posts of a 1-inch helical VTR with a brass dummy post, after running the sample tape wound 1410 m on a 26-inch reel for 96 minutes 50 times, The state of wear of the dummy posts was observed, and a relative value evaluation was made, with the most severe wear being set as 10 and the one with no wear being 0.

Video characteristics> Record and playback a single color chroma signal using a color video noise measuring device onto a 25.4 width sample tape loaded into a 1" helical VTR (type C), measure the AM noise component, and determine the color SN ratio. was calculated and expressed as a relative value to the standard tape.

(x) Average particle size of titanium oxide As is clear from the above table, the videotape of the present invention has
The carbon black and barium sulfate having a specific average particle size contained in the back coat layer provide excellent antistatic properties, anti-winding properties, and abrasion resistance.
It can also be seen that it is less likely to cause damage to the guide, etc., and can fully satisfy the original video characteristics.

Claims (1)

[Claims] (1) A magnetic recording medium characterized in that a back coat layer containing barium sulfate and carbon black with an average particle size of 0.2 to 2 μm is provided on the back side of a base having a magnetic layer on its main surface.