JPH0481262B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium that has excellent electromagnetic conversion characteristics, a low coefficient of friction, and good running durability. (Prior art) Recently, there has been an increasing demand for high-density recording in magnetic tapes for audio, video, computers, etc., and conventional Co-containing magnetic iron oxide has
Ferromagnetic alloy powder, which has become finer and finer,
Furthermore, ferromagnetic metal thin film magnetic recording media formed by vapor deposition methods such as vacuum evaporation, sputtering, and ion plating have been attracting attention and have been put into practical use. Furthermore, in the aforementioned magnetic recording tapes for audio, video, or computers, the surface of the magnetic layer is finished to be smooth in order to improve sensitivity (especially output in the high frequency range), and the tape has a thickness of about 20 μm. The following thin films are manufactured.
Therefore, the back layer is also thin and easily scratches, and furthermore, the strength of the entire tape is reduced due to thinning, which has an adverse effect on running durability, winding characteristics, dropout, etc. The inventors of the present invention have made extensive studies to solve these drawbacks, and have found that a significant improvement can be achieved by providing crater-like depressions on the surface of the back layer, resulting in the present invention. (Object of the Invention) That is, an object of the present invention is to provide a magnetic recording medium that does not increase the coefficient of friction, does not cause scratching, and has good running durability. Another object of the present invention is to provide a back layer that does not impair the S/N characteristics of the magnetic layer and is suitable for both general coated tapes and thin metal film magnetic tapes. (Structure of the Invention) The above object of the present invention is to provide a magnetic recording layer having a magnetic recording layer on the surface of a non-magnetic support, containing a filler and a binder on the opposite side, and having a back layer with a thickness of 2 μm or less. In the recording medium, crater-shaped depressions with an average diameter of 1.5 μm or less are formed on the surface of the back layer with an area of 10 μm.
This is achieved by providing 10 to 1000 pieces per square. In the present invention, a crater-shaped dent is defined as a clearly crater-shaped dent with an average diameter of 0.1 μm or more, as shown in a photograph taken using a scanning electron microscope and magnified 10,000 times the surface of the back layer of a magnetic recording medium. Refers to something that is recognized. The average diameter of the crater-like dents is 1.5 μm or less, preferably 0.08 to 1.2 μm.
m, particularly preferably 0.1 to 0.6 μm. or,
The number is preferably 10 to 1000, more preferably 20 to 500, even more preferably 25 to 400 per 10μ square.
It is individual. Also, the depth of the crater is the maximum depth
Preferably 0.01 μm or more and 1 μm or less, more preferably 0.01 μm or more and 0.5 μm or less, and even more preferably 0.01 μm.
m or more and 0.4 μm or less. By providing the above-mentioned craters in the back layer, the craters serve as a lubricant reservoir and provide a sustained lubricating effect. If the average diameter of the crater depression exceeds 1.5 μm, it will cause an impression on the magnetic layer, which will adversely affect the electromagnetic conversion characteristics.
Further, the number of craters similarly has a bad effect on the electromagnetic conversion characteristics, and should not be too large or too small. For areas other than craters, it is desirable that they be smooth, and in terms of center line average roughness Ra, Cut off is 0.08.
It is preferably 0.03 μm or less in mm. The above-mentioned crater-shaped depressions can also be created by spraying water immediately after application and before drying when applying the back layer coating solution, or by passing through a zone where the humidity is 70% RH or higher. However, this can also be achieved by adding a small amount of a poor solvent to the back layer coating solution. As the binder for the back layer, use may be made of binders conventionally known in the art, such as thermoplastic resins, thermosetting resins, reactive resins, or mixtures thereof. For example, you can choose from the binders shown below, but it is desirable that the glass transition temperature Tg of one type or a mixture of two or more types is 40°C or higher, and especially Tg of 60°C or higher. is preferred. Examples of thermoplastic resins include vinyl chloride-vinylacetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, and acrylic ester-acrylonitrile copolymer. ,
Acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer,
Methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-
Acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose resin (cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid These include ester copolymers, amino resins, and various rubber resins. Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins,
These include acrylic reactive resins, polyisocyanates, and polyamines. The fillers for the back layer used in the present invention include the following. Carbon black, graphite, tungsten disulfide, molybdenum disulfide, boron nitride, silicon oxide, calcium carbonate, α-alumina, red iron oxide, titanium oxide (titanium white or titanium black), zinc oxide,
Powders such as barium sulfate, tin oxide silicon carbide, and magnesium carbonate may be used, but inorganic powders other than those listed above may also be used. Among the above, carbon black, calcium carbonate, α-alumina, red iron oxide, titanium oxide,
These include barium sulfate and tin oxide. These may be used alone or in combination of two or more. The ratio of filler to binder in the back layer used in the present invention is preferably 1/0.5 to 1/3.5 by weight. More preferably, it is 1/0.8 to 1/3.0. If the ratio of filler to binder is too large, powder will easily fall off, while if the ratio of filler is too small, the coefficient of friction will increase. In addition, the back layer of the present invention may be coated with a lubricant used in ordinary magnetic tapes or overcoated, but especially fatty acids having 12 or more carbon atoms and their metals may be used. Running properties can be further improved by using salts and esters. The magnetic recording medium of the present invention is
It can be prepared using the materials and manufacturing method described in No.-26890. (Example) Next, an example of the present invention will be described. In the examples, "parts" indicate "parts by weight." Example 1 A 5-μm-thick magnetic layer containing Co-containing magnetic iron oxide was provided on the surface of a 14-μm-thick polyethylene terephthalate base, and a back layer was coated on the opposite surface to a dry thickness of 1 μm. The magnetic layer and back layer have the following compositions. <Magnetic layer coating liquid> Co-containing magnetic iron oxide (S _BET 35m ² /g) 100 parts Nitrocellulose 10〃 Polyurethane resin (product name "Nitsuporan 2304")
8. Polyisocyanate 8. Cr ₂ O ₃ 2. Carbon black (average particle size 20 μm) 2. Stearic acid 1. Butyl stearate 1. Methyl ethyl ketone 300 parts <Back layer coating liquid> Carbon black (particle size 50 μm) 100 parts Nitro Cellulose 60〃 Polyurethane resin (product name "Nituporan 2301")
60〃 Polyisocyanate 40〃 Zinc stearate 1〃 Cr ₂ O ₃ 1〃 Methyl ethyl ketone 600〃 When applying the back layer, the humidity from the application area to the drying zone was set to 70% RH, and the residence time was changed as needed to adjust the size of the crater. I've adjusted the numbers. The obtained samples are designated as No. 1 to No. 11. Example 2 Co-Ni (Ni: 20 wt%) was deposited on the surface of a 12 μm thick polyethylene terephthalate base by oblique vapor deposition.
A magnetic film (thickness: 0.15 μm) was provided, and a back layer was provided on the opposite side. The back layer was the same as in Example 1. However, the back layer was overcoated with stearic acid and butyl stearate. The obtained samples are designated as No. 12 to No. 15. The following tests were conducted on each sample of the above magnetic tape, and the results shown in Table 1 were obtained. Test method (1) Coefficient of friction Regarding tape slit to 1/2 inch width
Rub the stainless steel pole on the back layer surface at a speed of 3.3 cm/s with T ₁ load of 50 g to find T ₂ T ₂ /T ₁
issued. Measurements were made using virgin samples and a VHS type VTR.
This was done on samples after running 100 passes and samples after running 1000 passes. The friction coefficient μ was calculated using the following formula. μ=1/πlnT ₂ /T ₁ (2) Color S/N A noise meter (925C) manufactured by Shibasoku was used as the measuring device, and the reference tape was sample No. 1.
~ In No. 11, sample No. 1 is set to 0 dB,
For samples No. 12 to No. 15, sample No. 12
was set as 0 dB, and the difference in S/N ratio was determined. Virgin tape was used as the measurement sample.
High pass filter 10KHz, low pass filter 500KHz, AM. The VTR used was a Matsushita NV-8300.

[Table] As is clear from Table 1, the coefficient of friction of the back layer provided with crater-shaped depressions of the present invention does not increase significantly even when it is repeatedly run. Moreover, color S/N is also good.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of the surface of the back layer of the present invention at a magnification of 10,000 times.

Claims (1)

[Claims] 1. In a magnetic recording medium having a magnetic layer on one side of a non-magnetic support, a filler and a binder on the opposite side, and a back layer with a thickness of 2 μm or less, the surface of the back layer has a magnetic layer with an average diameter. A magnetic recording medium characterized by having 10 to 1000 crater-like depressions of 1.5 μm or less per 10 μm square.