JPH0249487B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a ferromagnetic metal thin film type magnetic recording material, particularly a magnetic tape, by providing a coating film mainly composed of a resin material on the opposite surface of the base film to the magnetic layer, thereby improving running performance of the magnetic tape, preventing static electricity, and improving high temperature and high humidity. The purpose is to improve corrosion resistance and blocking resistance under environmental conditions. Metal thin film type magnetism 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. Tape is 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 and humid atmospheres.
In particular, if the tape is wound up on a reel or hub and subjected to sudden temperature changes under high humidity, condensation is likely to form between the opposing magnetic surfaces and the back side of the wound tape. Since the gap between the magnetic surface and the back surface is narrow, the water droplets formed by condensation are difficult to evaporate and remain wet on the magnetic surface for a long time, which tends to cause corrosion, and when the corroded area dries,
It has become clear that the magnetic surface and the back surface tend to adhere (blocking) through 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 the metal thin film magnetic tape satisfies the general characteristics of magnetic tapes such as slipperiness, prevention of scratching, and prevention of static electricity. must be addressed. 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. Organic surfactants such as anionic surfactants, cationic surfactants, and nonionic surfactants that have been conventionally used in coated magnetic tapes have good affinity with water, so they prevent rust from forming. This was unsuitable from the point of view of rust prevention. 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, potassium, lithium, and calcium esters. , higher fatty acid metal salts such as barium, zinc, magnesium, aluminum, lead, chromium, cobalt, nickel copper, iron, tin, mercury salts, and higher aliphatic alcohols such as lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, Laurylic acid amide, myristic acid amide, palmitic acid amide,
A higher fatty acid amide such as stearic acid amide is used. 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. Polyurethane is used as the binder resin because it has excellent compatibility with antistatic agents, lubricants, and water repellents, and excellent dispersibility of solid particles. Further, a small amount of other resin may be mixed with polyurethane. By incorporating nitrocellulose, blocking resistance and solvent removal properties during coating are improved. Stearic acid and graphite were added to polyurethane, a solvent was added, and a dispersion treatment was performed using a ball mill to create a coating solution. The coating material was applied to the back side of a metal thin film type magnetic tape in which a cobalt alloy was vapor-deposited on a polystyrene terephthalate film. This tape showed no occurrence of rust or blocking even under high temperature and high humidity environmental conditions. Furthermore, when the vehicle was run using a video tape recorder, the running was stable and there was no noise caused by charging. Examples of the present invention will be specifically described below. Example The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Nitsuporan 3004 (polyurethane manufactured by Nippon Polyurethane Industries, Ltd.) 200 parts Carbon black 100 parts Molybdenum disulfide 100 parts Pentaerythritol tetrastearate 4 parts Nitrocellulose RS-1/2 (manufactured by Daicel Chemical Industries, Ltd.) 50 parts Ethyl acetate 1300 parts Cyclohexanone 400 parts Thereafter, the following composition was added, and the mixture was further stirred and dispersed in a ball mill for 8 hours to obtain a paint. Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) 20 parts Ethyl acetate 200 parts Cyclohexanone 100 parts Cobalt (80
%), was applied to the back side of a nickel (20%) ferromagnetic alloy thin film. After drying, it was cut to an appropriate width to create a magnetic tape. The coating film thickness was 3.8μ. Comparative Example A The following composition was placed in a ball mill and stirred for 40 hours to perform a dispersion treatment. Nitsuporan 2301 (manufactured by Nippon Polyurethane Industry Co., Ltd.)
One-component polyurethane) 100 parts Graphite ASSP (manufactured by Nippon Graphite Industries Co., Ltd.)
300 parts Stearic acid 1 part Ethyl acetate 2000 parts Cyclohexanone 1000 parts Cobalt (80%
%), was applied to the back side of a nickel (20%) ferromagnetic alloy thin film. After drying, it was cut to an appropriate width to create a magnetic tape. The coating film thickness was 4.2μ. Comparative Example B The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Nitsuporan 3004 (polyurethane manufactured by Nippon Polyurethane Industries Co., Ltd.) 100 parts Carbon black 300 parts Carbon fluoride 30 parts Calcium stearate 5 parts Methyl ethyl ketone 400 parts Toluene 900 parts Ethyl acetate 500 parts Then, the following composition was added and further processed in a ball mill. The mixture was stirred for 8 hours and subjected to dispersion treatment to obtain a paint. Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) 20 parts Methyl ethyl ketone 100 parts Toluene 100 parts Cobalt (80
%), was applied to the back side of a nickel (20%) ferromagnetic alloy thin film. After drying, it was cut to an appropriate width to create a magnetic tape. The coating film thickness was 4.0μ. This is designated as sample B. Comparative Example C The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Nitsuporan 3022 (polyurethane manufactured by Nippon Polyurethane Industry Co., Ltd.) 200 parts Carbon black 200 parts Palmityl alcohol 4 parts Methyl ethyl ketone 500 parts Toluene 1000 parts Then, the following composition was further added, stirred in a ball mill for 8 hours, and dispersed. It was made into a paint. Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) 15 parts Methyl ethyl ketone 100 parts Toluene 100 parts Cobalt (80
%) was applied to the surface of a nickel (20%) ferromagnetic alloy thin film. After drying, it was cut to an appropriate width to create a magnetic tape. The coating film thickness was 3.2μ. This is designated as sample C. Comparative Example D The following composition was charged into a ball mill and stirred for 40 hours to perform a dispersion treatment. Nitsuporan 2304 (polyurethane manufactured by Nippon Polyurethane Industries Co., Ltd.) 150 parts Graphite ASSP (manufactured by Nippon Graphite Industries Co., Ltd.)
200 parts Stearamide 3 parts Ethyl acetate 1500 parts Cyclohexanone 1500 parts Cobalt (80
%), was applied to the back side of a nickel (20%) ferromagnetic alloy thin film. After drying, it was cut to an appropriate width to create a magnetic tape. The coating film thickness was 3.7μ. This is designated as sample D. Samples A and B created in the above examples and comparative examples,
An environmental test was conducted by leaving samples C, D and uncoated samples wound on a reel at a temperature of 60° C. and a humidity of 90%. In addition, the contact angle of the coating film with water was measured to examine water repellency. The results are shown in the table below.

[Table] As is clear from the table, the material according to this example has the highest contact angle with water, and its water repellency prevents moisture from penetrating and improves corrosion resistance the most. Furthermore, a running test was conducted using a test machine that has the same functionality as a commercially available VCR. For samples with uncoated back side,
Although running was unstable and noise caused by triboelectric charging was occasionally observed, each sample A of the example and comparative example
In B, C, and D, running was stable, and no noise caused by triboelectric charging was observed. 10g on mirror finished stainless steel block
Frictional resistance was measured under a load of . The table shows the frictional resistance of each sample of Examples and Comparative Examples, assuming that the frictional resistance of the sample with no coating on the back side is 1.00.

【table】

[Table] As is clear from the table, the product according to this example has low frictional resistance and excellent lubricity. As described above, according to the present invention, by forming a coating film made of polyurethane containing graphite or carbon black, higher fatty acids, etc., molybdenum disulfide or carbon fluoride, and nitrocellulose on the surface of the substrate, Not only corrosion resistance but also blocking resistance can be easily improved, and the ability to remove solvents during coating can also be improved.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic substrate, at least one of graphite and carbon black, a higher fatty acid, a higher fatty acid ester, a higher At least one selected from the group consisting of fatty acid metal salts, higher fatty acid amides, and higher fatty acid alcohols, and molybdenum disulfide or carbon fluoride;
1. A magnetic recording medium comprising a coating film made of polyurethane containing nitrocellulose.