JPH0249489B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a ferromagnetic metal thin film type magnetic recording medium with a coating film mainly made of a resin material on the opposite side of the magnetic layer of the base film, thereby improving running performance of the magnetic recording medium, preventing static electricity, and improving environmental conditions under high temperature and humidity. The purpose is to improve corrosion resistance and blocking resistance under the surface. A metal thin film type film obtained by forming a ferromagnetic thin film mainly composed of iron, cobalt, nickel, or an alloy thereof on a polymer film support such as polyester or polyimide by vacuum evaporation, sputtering, ion plating, etc. Magnetic recording media are ideal for high-density recording, such as recording video signals. However, metal thin films generally have a problem of poor corrosion resistance in high-temperature, high-humidity environments, especially when exposed to rapid temperature changes in high humidity while being rolled up in tape form on reels, hubs, etc. , dew condensation easily occurs between the opposing magnetic surfaces and the back surface in the rolled-up state, and once condensation occurs, the gap between the magnetic surface and the back surface is narrow, making it difficult for water droplets to evaporate and leave the magnetic surface wet for a long time. It has become clear that corrosion tends to occur in that area, and when the corroded area dries, the magnetic surface and back surface tend to adhere (blocking) through the corrosion products. If the surface properties of the magnetic surface are improved in order to increase the recording density, the gap between the magnetic surface and the back surface in the rolled-up state will become smaller, and the above phenomenon will become even more pronounced. The back side of a metal thin film type magnetic recording medium satisfies the general characteristics of magnetic recording media such as slipperiness, anti-erosion, and antistatic properties, and as mentioned above, it is free from rust and corrosion caused by rust. We have to deal with the blocking phenomenon. From this point of view, as a result of examining various materials, a material with excellent blocking resistance and rust prevention effect was discovered. The basic constituent materials of the present invention include antistatic agents,
Consists of water repellent, lubricant, and binding resin. As the antistatic agent in the present invention, a solid antistatic agent such as carbon black or particulate graphite is used. Conventionally, organic surfactants such as anionic surfactants, cationic surfactants, and nonionic surfactants that have been used in coated magnetic tapes have good affinity with water, so they prevent the formation of rust. This was unsuitable from the standpoint of rust prevention. In the present invention, carbon black and graphite control the roughness of the surface of the coating film, and together with the water repellent, prevent the infiltration of moisture and prevent the blocking phenomenon caused by corrosion. The appropriate amount of carbon black and graphite to be mixed is 75 to 100 parts by weight per 100 parts by weight of polyester. If the amount is less than 75 parts by weight, not only will antistatic properties become insufficient, but the surface roughness of the coating film will become small, and blocking phenomenon will likely occur. If the amount is more than 100 parts by weight, the strength of the coating film will be insufficient, causing powder to fall off during running, and in severe cases, peeling of the film. In addition, water repellent agents include higher fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, and oleic acid, their alcohol esters, higher fatty acid esters such as polyhydric alcohol esters, and their sodium salts, potassium salts, and lithium salts. , calcium salts, barium salts, zinc salts,
Higher fatty acid metal salts such as magnesium salts, aluminum salts, lead salts, chromium salts, cobalt salts, nickel salts, copper salts, iron salts, tin salts, and mercury salts, and higher fatty acid metal salts such as lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, etc. Fatty alcohols and higher fatty acid amides such as lauric acid amide, myristic acid amide, and palmitic acid amide are used. In the present invention, the water repellent agent not only improves the water repellency of the coating surface, but also transfers to the surface of the magnetic layer when wound on a reel, etc., and is adsorbed onto the surface of the ferromagnetic metal thin film that makes up the magnetic layer. It also improves the water repellency of the surface of the magnetic layer, prevents moisture from entering under high humidity conditions, and improves corrosion resistance. The appropriate amount of water repellent to be mixed is 2.0 to 2.7 parts by weight per 100 parts by weight of polyester.
If the amount is less than 2.0 parts by weight, a sufficient water repellent effect cannot be obtained. If the amount is more than 2.7 parts by weight, the excess water repellent may fall off or may be transferred to the surface of the magnetic layer, causing it to stick to the post or cylinder during recording or playback on a video tape recorder. may occur, making driving unstable. graphite, higher fatty acids, higher fatty acid esters, higher fatty acid metal salts, higher fatty alcohols,
Higher fatty acid amides have excellent lubricity, but the lubricity can be further improved by adding a solid lubricant such as molybdenum disulfide or carbon fluoride. A thermoplastic polyester having excellent compatibility with antistatic agents, lubricants, and water repellents and excellent dispersibility of solid particles is used as the feedstock resin. Further, a small amount of other resin may be mixed with the thermoplastic polyester.
By incorporating nitrocellulose, blocking resistance and solvent removal properties during coating are improved. Stearic acid and graphite were added to thermoplastic polyester, a solvent was added, and a dispersion process was performed using a ball mill to create a coating solution. The coating solution was applied to the back side of a metal thin film type magnetic recording medium in which a cobalt alloy was deposited on a polyethylene terephthalate film. This magnetic recording medium showed no occurrence of rust or blocking even under high temperature and high humidity environmental conditions. When I ran it using a video tape recorder, it ran stably and there was no noise caused by charging. Examples of the present invention will be specifically described below. Example 1 The following composition was charged into a ball mill, stirred for 40 hours, and subjected to dispersion treatment. Byron 200 (thermoplastic polyester manufactured by Toyobo Co., Ltd.) 100 parts by weight Graphite ASSP (manufactured by Nippon Graphite Industries Co., Ltd.)
80 parts by weight Stearic acid 2.0 parts by weight Methyl ethyl ketone 120 parts by weight Toluene 600 parts by weight Cyclohexanone 40 parts by weight The obtained paint was coated with a bar coater on a polyester film using a vacuum evaporation method to form a ferromagnetic alloy thin film of 80% cobalt and 20% nickel. Coated on the back.
After drying, it was cut into a suitable width to produce a magnetic recording medium. The coating film thickness was 3.0μ. This is designated as sample A. Example 2 The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Byron 300 (thermoplastic polyester manufactured by Toyobo Co., Ltd.) 100 parts by weight Carbon black 100 parts by weight Molybdenum disulfide 33 parts by weight Pentaerythritol tetrastearate
2.7 parts by weight Nitrocellulose 33 parts by weight Ethyl acetate 533 parts by weight Methyl ethyl ketone 533 parts by weight Toluene 533 parts by weight
It was applied to the back side of a 20% nickel ferromagnetic alloy thin film. After drying, it was cut into a suitable width to produce a magnetic recording medium. The coating film thickness was 5.0μ. This is designated as sample B. Example 3 The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Byron GXW (thermoplastic polyester manufactured by Toyobo Co., Ltd.) 100 parts by weight Carbon black 100 parts by weight Carbon fluoride 10 parts by weight Calcium stearate 2.0 parts by weight Methyl ethyl ketone 200 parts by weight Toluene 750 parts by weight Cellosolve acetate 150 parts by weight The obtained paint 80% cobalt made by vacuum evaporation method on polyester film with bar coater.
It was applied to the back side of a 20% nickel ferromagnetic alloy thin film. After drying, it was cut into a suitable width to produce a magnetic recording medium. The coating film thickness was 4.2μ. This is designated as sample C. Example 4 The following composition was charged into a ball mill and stirred for 48 hours to perform a dispersion treatment. Byron 540 (thermoplastic polyester manufactured by Toyobo Co., Ltd.) 100 parts by weight Carbon Black 100 parts by weight Palmityl alcohol 2.5 parts by weight Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) 7.5 parts by weight Methyl ethyl ketone 250 parts by weight Toluene 750 parts by weight 100 parts by weight of cyclohexanone The resulting paint was coated with 80% cobalt, which was created by vacuum deposition on a polyester film using a bar coater.
It was applied to the back side of a 20% nickel ferromagnetic alloy thin film. After drying, it was cut into a suitable width to produce a magnetic recording medium. The coating film thickness was 3.8μ. This is designated as sample D. Example 5 The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Byron 300 (thermoplastic polyurethane manufactured by Toyobo Co., Ltd.) 100 parts by weight Graphite ASSP (manufactured by Nippon Graphite Industries Co., Ltd.)
75 parts by weight Stearic acid amide 2.5 parts by weight Ethyl acetate 400 parts by weight Methyl ethyl ketone 400 parts by weight Toluene 400 parts by weight The resulting paint was coated with a bar coater and coated with 80% cobalt, which was created by vacuum deposition on a polyester film.
It was applied to the back side of a 20% nickel ferromagnetic alloy thin film. After drying, it was cut into a suitable width to produce a magnetic recording medium. The coating film thickness was 3.0μ. This is designated as sample E. As a comparative example, a magnetic recording medium in which graphite was not mixed was prepared in Example 1, and this was designated as Sample F. Further, as a comparative example, a magnetic recording medium in which stearic acid was not mixed was prepared in Example 1, and this was designated as Sample G. When the samples A, B, C, D, and E prepared in Examples 1, 2, 3, 4, and 5, the comparative examples F and G, and the samples with no back surface coating were wound on a reel, the temperature
An environmental test was conducted by leaving the product under conditions of 60°C and 90% humidity. In addition, the contact angle with water on the surface of the magnetic layer and the surface of the back coating was measured to examine water repellency. The results are shown in the table below.

[Table] Antenna As is clear from the table, the material according to the present invention contains a water repellent, so when it is wound up on a reel, it is transferred to the surface of the magnetic layer, making it difficult to resist water on both sides of the magnetic recording medium. The contact angle is increased, preventing moisture from entering and improving the corrosion resistance of the magnetic thin film. Furthermore, a running test was conducted using a test machine that has the same functionality as a commercially available video tape recorder. In the sample whose back side was not coated, running was unstable, and noise, which was thought to be caused by triboelectric charging, was occasionally observed. Further, in Comparative Example Sample F, the running was stable at the beginning, but the running gradually became unstable. On the other hand, in Examples A, B, C, D, and E, running was stable, and no noise thought to be caused by triboelectric charging was observed. Furthermore, frictional resistance was measured with a 10g load on a mirror-finished stainless steel block. The table shows the frictional resistance of each sample, assuming that the frictional resistance of the uncoated sample on the back side is 1.00.

[Table] As is clear from the table, the product according to the present invention has low frictional resistance and excellent lubricity. As described above, according to the present invention, corrosion resistance and blocking resistance can be easily improved.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic substrate, 75 to 100 parts by weight of at least one of graphite and carbon black is added to the surface of the non-magnetic substrate opposite to the ferromagnetic metal thin film. , 100 parts by weight of a thermoplastic polyester containing at least one selected from the group consisting of , 2.0 parts by weight to 2.7 parts by weight of higher fatty acids, higher fatty acid esters, higher fatty acid metal salts, higher fatty acid amides, and higher fatty acid alcohols. A magnetic recording medium characterized by forming a coating film consisting of.