JPH03168920A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve qualities of reproduced signals by providing a metal magnetic layer on the one side of a nonmagnetic substrate and a back coating layer containing a fluorocarbon lubricant on the other side of the substrate, and further incorporating an antistatic into the back coating layer. CONSTITUTION:An antistatic is incorporated into the back coating layer containing a fluorocarbon lubricant. Any antistatics can be used if they have the effect to chemically raise the moisture absorption of the surface of org. polymer material such as plastics and to reduce the leaked surface resistivity to <=10<10>OMEGA to effectively inhibit charging. For example, when a siloxane antistatic is used, the back coating layer is cured while absorbing moisture in air, and after the layer is enough cured, it still contains a small amt. of silanol groups which give moisture absorption. Thus, the leaked surface resistivity of the layer can be decreased to about 10<9>OMEGA order.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, and particularly to magnetic recording media such as running properties and durability. This article relates to magnetic recording media with excellent antistatic effects. E Summary of the Invention] The present invention provides a metal magnetic Fitl on one surface of a non-magnetic support.
! In a so-called metal thin film type magnetic recording medium in which a magnetic layer consisting of J is formed and a back coat layer holding a fluorocarbon lubricant is formed on the other side, by making the Banok coat layer hold an antistatic agent. , an object of the present invention is to provide a magnetic recording medium that maintains good runnability and durability while effectively preventing charging even when used in sliding contact with a guide member made of an organic polymer material, etc. It is.

[Conventional technology]

In recent years, with the increasing demand for high-density magnetic recording, so-called metal thin films have been developed, in which magnetic materials made of metals or alloys are directly deposited on non-magnetic supports using plating or vacuum thin film forming techniques to form metal magnetic thin films. type magnetic recording media are becoming widely used.

This metal thin film type magnetic recording medium has a high coercive force. Excellent squareness ratio, electromagnetic conversion characteristics in the short wavelength range, etc., the thickness of the magnetic layer can be made extremely thin, so the thickness loss during recording demagnetization and reproduction is extremely small, and polymer bonding in the magnetic layer Since it does not contain non-magnetic materials such as agents, it has many advantages such as being able to increase the packing density of magnetic materials.

By the way, since magnetic recording media are used in sliding contact with the magnetic head, guide member, etc. of a recording/reproducing device, they are stable and excellent! In order to exhibit magnetic conversion characteristics, running properties, durability, etc. must be good. Therefore, it is widely practiced to provide a back coat layer on the side opposite to the magnetic layer on the nonmagnetic support. This backcoat layer is formed by applying a backcoat paint consisting of a polymeric binder and a nonmagnetic conductive material dispersed in an organic solvent. The conductive material mentioned above is acetylene black.
By-product black 1 Carbon-based materials such as carbon black are typical.

In addition, various lubricants are used to improve running performance. Efforts are also being made to improve durability. This lubricant is mainly used to reduce the coefficient of friction between the magnetic layer and other sliding members such as the magnetic head or guide member by adding it internally to the magnetic layer or coating the surface of the magnetic layer. However, since some guide members etc. come into sliding contact with the back coat layer side of the magnetic recording medium, lubricants are sometimes added internally or coated on the back coat layer. As a lubricant, in addition to higher fatty acids and their esters, in recent years, perfluoroboriethers have been used as lubricants. Fluorocarbon lubricants such as barfluorocarboxylic acid esters and barfluoroalkyl carboxylic acid esters and ammonium salts of barfluorocarboxylic acids have attracted attention for their good properties and are now widely used. [Problem to be Solved by the Invention] Incidentally, since the magnetic layer of a metal thin film type magnetic recording medium is made up of only highly conductive metals, it is inherently difficult for charging to occur. It is generally understood that even if there is a factor that causes charging, it is sufficiently avoided by the conductive material contained in the back coat layer.

However, when the above-mentioned fluorocarbon lubricant was actually applied to, for example, a metal thin film type video tape, a phenomenon in which part of the image was periodically disturbed during playback was observed. This is thought to be because the videotape becomes charged for some reason, and when the accumulated charge reaches a certain amount, a discharge occurs. Studies have shown that this phenomenon is caused by the presence of an insulating fluorocarbon lubricant in the gap between the sliding contact between the guide member made of polyoxymethylene (POM) resin, etc. and the Bathoku coat layer, which promotes charging. It has become clear that. Furthermore, it has become clear that such charging increases the coefficient of kinetic friction. For example, when measuring the coefficient of dynamic friction against a POM resin guide pin for magnetic recording media with and without perfluoroboryether applied as a fluorocarbon lubricant on the surface of the back coat layer, the former has a higher value. It has been experimentally confirmed that replacing the guide bin with a metal one can suppress the increase in the coefficient of dynamic friction. In other words, electrification is a contributing factor to increased friction, and the fluorocarbon lubricant, which is originally used to reduce friction, has the opposite effect.

Therefore, an object of the present invention is to provide a magnetic recording medium that allows the fluorocarbon lubricant to exhibit its original functions while also preventing static electricity.

[Means for solving the problem] As a means to prevent the magnetic recording medium from being charged as described above, it is possible to change the material of the guide pin from polymer to metal, or to make the magnetic recording medium less likely to be charged. It is possible to improve this. However, the inventors' studies have revealed that the former method makes it difficult to reduce the weight and cost of the recording/reproducing device, whereas the latter method can be easily achieved by using an antistatic agent. It became clear that it could be done. The magnetic recording medium according to the present invention is proposed based on the above-mentioned findings, and includes a magnetic layer made of a metal magnetic thin film formed on one side of a non-magnetic support, and a fluorocarbon-based lubricant on the other side. This magnetic recording medium is provided with a hank coat layer that retains an antistatic agent, and is characterized in that the back coat layer retains an antistatic agent.

First, regarding the structure of the magnetic recording medium to which the present invention is applied, particularly regarding the non-formal aspects of the magnetic layer, a fluorocarbon lubricant and an antistatic agent are either added internally or coated on the surface. There are several types that can be considered depending on whether they are retained in the coating layer, but the following four types are particularly effective. That is, ■ a back coat layer containing a conductive material. A three-layer structure in which a fluorocarbon lubricant coating and an antistatic agent coating are sequentially laminated.
■Back coat layer containing conductive material and fluorocarbon lubricant. A two-layer structure in which a coating film containing a fluorocarbon lubricant and an antistatic agent is sequentially laminated; ■ A two-layer structure in which a buff coat layer containing a conductive material and a coating film containing a fluorocarbon lubricant and an antistatic agent are sequentially laminated; and ■ Conductive. Materials and fluorocarbon lubricants. It has a single layer structure in which a hank coat layer containing an antistatic agent is formed. In addition, a structure in which a coating film containing only a fluorocarbon lubricant is disposed on a layer containing a conductive material and an antistatic agent is considered, but this does not meet the purpose of the present invention for the reasons described above.

As the fluorocarbon lubricant, per-7 fluoropolyether. Perfluorocarboxylic acid ester, carboxylic acid perfluoroalkyl ester. Conventionally known compounds such as perfluorocarboxylic acid ammonium salts can be used. When the above-mentioned lubricant is internally added to the back coat layer, 0.2 to 20 parts by weight per 100 parts by weight of the binder.
It is desirable to add within the range of parts by weight. When the lubricant is applied to the surface of the back coat layer, the amount of the lubricant applied is 0.5 to 100 mg/m'', more preferably 1 to 20 mg/m''. As the above-mentioned antistatic agent, antistatic agents generally used in the field of antistatic coatings for plastics are suitable. This is because an organic polymer material is used as a binder for the conductive material powder in the back coat layer.
This is also to obtain an antistatic effect on the sliding contact member made of organic polymer inside the recording/reproducing device. Suitable materials include natural surfactants such as saponin, alkylene oxides, and glycerin. Nonionic surfactants such as glycidol, higher alkyl amines, quaternary ammonium salts,
Heterocyclic compounds such as pyridine, cationic surfactants such as phosphonium or sulfonium, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric esters, phosphoric esters, amino acids, aminosulfonic acids, amino acids, etc. Examples include amphoteric activators such as sulfuric acid or phosphoric acid esters of alcohols.

Alternatively, siloxane-based antistatic agents can also be used. This is a colloidal dispersion of a Si-0-St chain or a compound having a crosslinked structure thereof, and is commercially available from Colcoat Company under the trade name Colcoat.

The amount of the antistatic agent used is selected within a range of about 1% by weight to about the same amount as the amount of the fluorocarbon lubricant used. If the amount is less than the above range, the desired antistatic effect cannot be expected, and if the amount is more than the amount of lubricant used, there is a risk that the running properties will be deteriorated.

In the present invention, the above-mentioned conductive material and antistatic agent are added to the back coat layer, but other conventionally commonly used nonmagnetic powders may be used in combination, if necessary. This non-magnetic powder includes hematite, mica, silica gel, magnesium oxide, zinc sulfide, tungsten carbide, boron nitride, starch, zinc oxide, kaolin, talc, clay, lead sulfate, barium carbonate, calcium carbonate, magnesium carbonate, and boehmite. (T-A2.○,・H20)
, alumina, tungsten sulfide, titanium oxide, polytetrafluoroethylene powder, polyethylene powder, polyvinyl chloride powder, metal powder, etc.

In addition, the binder mixed into the back coat layer, various additives such as dispersants, abrasives, and rust preventives used as necessary, and the materials used for the non-magnetic support and magnetic exposure are conventional. Any known method can be applied and is not limited in any way.

[Function] The ease with which a substance placed in the air is charged can be evaluated by the surface leakage resistance value of the substance. This value is 1
There are many substances known as electrical insulators with a resistance of 01'1Ω or more, and many plastic materials, such as organic polymer materials, have an electrical resistance of about 10' to 10'6 Ω at room temperature. It is an insulator. However, this value is known to decrease as the humidity in the air increases.

The above-mentioned antistatic agents used in the present invention all have the effect of increasing the hygroscopicity of the surface of organic polymer materials by chemical methods, and are extremely effective by reducing the surface leakage resistance value to 1016Ω or less. It is a substance that can suppress static electricity. In other words, various surfactants are oriented so that the hydrophobic part faces the hydrophobic component such as the binder or fluorocarbon lubricant contained in the back coat layer, and the hydrophilic group faces the opposite side. Increases the moisture absorption of Hank Coat's own surface. In addition, siloxane-based antistatic agents cure while absorbing moisture in the air, but even after they are fully cured, they still have some silanol groups, and their hygroscopicity reduces the surface leakage resistance to about 10'Ω. can be reduced to the order of .

A magnetic recording medium in which such an antistatic agent is retained in the Banok coating layer does not increase the coefficient of dynamic friction even when it comes in sliding contact with a guide member made of an organic polymer such as POM, and has good running properties. It exhibits durability and does not generate noise due to discharge of accumulated charges during playback.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental examples.

Example 1 In this example, a Banko-F layer containing a carbon blank as a conductive material and a coating film containing a fluorocarbon lubricant and an antistatic agent were laminated on the non-shaped surface of the magnetic layer. This is an example of a deotave. The above videotape was created as follows. first,
Co is deposited on one side of a 10 μm thick polyethylene terephthalate (PET) film by oblique vapor deposition,
A ferromagnetic metal thin film with a thickness of 1000 nm was formed. moreover,
A fluorocarbon lubricant was applied to the surface of the above ferromagnetic metal thin film at a concentration of 0.1% by weight.
F. ) was coated with a 7% soluble paint.

Next, a backcoat layer paint for forming the backcoat layer was prepared according to the following guidelines. Carbon black polyurethane resin (manufactured by Nippon Polyurethane Co., Ltd., trade name N-2304) Methyl ethyl ketone Methyl isobutyl ketone Toluene 60 parts by weight 30 parts by weight 70 parts by weight 70 parts by weight 70 parts by weight The above Banok Coat N paint was applied to the other side of the above PET film, That is, the ferromagnetic metal thin film was coated non-formally or directly and dried to form a hank coat layer having a layer thickness of 3 μm.

Next, a paint containing perfluoroboriether (trade name Fontprin AM2001, manufactured by Montegisson) as a fluorocarbon-based lubricant and an antistatic agent (trade name Colcoat 515, manufactured by Colcoat) as an antistatic agent was prepared, and the above-mentioned It was applied on top of the backcoat layer.

Thereafter, it was subjected to ordinary magnetic field orientation treatment, calender treatment, etc., and then cut into 1/2 inch width to prepare a sample tape.

Example 2 This example describes a video tape in which a back coat layer containing Rikibon black, a coating film of a fluorocarbon lubricant, and a coating film of an antistatic agent are sequentially laminated on the non-formed surface of the magnetic layer. This is an example.

The above videotape was created as follows.

First, the magnetic layer and back coat layer were prepared in the same manner as in Example 1. Next, apply the same fluorocarbon lubricant as described above to the surface of the Hasoku coat layer at a concentration of 0.1% by weight.
13 (C.CffilF.) was applied, and then the same antistatic agent as above was applied. after that,
A sample table was made using the same process.

Comparative Example 1 This comparative example is an example of a video tape in which only a back coat layer containing a carbon blank was formed on the non-formed side of the magnetic layer, and no fluorocarbon lubricant or antistatic agent was used. A magnetic layer and a back coat layer were formed on a PET film according to the method described above in Example 1, and a sample tape was prepared. Comparative Example 2 In this comparative example, a coating film of a fluorocarbon moisturizer is laminated on a back coat layer containing Riki-Ponrank on the amorphous surface of the magnetic layer, and no antistatic agent is used. This is an example of a videotape.

On the back coat layer of the sample tape prepared in Comparative Example 1, the fluorocarbon lubricant paint described above in Example 2 was further applied in the same manner to prepare a sample tape.

The sample tapes obtained in each of the above Examples and Comparative Examples were subjected to measurement of dynamic friction coefficient, shuttle running test, and observation of discharge phenomenon.

The coefficient of dynamic friction is 5 mm when a constant tension is applied to the sample tape after running the shuttle 100 times at room temperature and humidity.
Measurements were made by running the tape in sliding contact with a POM guide pin at a tape speed of /second. In the shuttle running test, a video deck (manufactured by Sony,
EVF 900) was used to perform 100 shuttle runs at room temperature, and the presence or absence of adhesion between the magnetic layer and the back coat layer was examined.

The discharge phenomenon was also observed by examining the presence or absence of periodic disturbances in the image during playback. The above results are shown in Table 1.

Table 1 First, in Comparative Example 1, in which the fluorocarbon lubricant is not retained in the back coat layer, the coefficient of dynamic friction is kept low because charging is difficult to occur, but sticking occurs after less than 20 shuttle runs. did. Here, a similar lubricant is applied to the surface of the metal magnetic thin film that is the magnetic layer, but since the lubricant is not retained in the hasok coat layer, the lubricant is transferred from the magnetic layer to the back coat layer. It is thought that this caused the amount of lubricant on the magnetic layer side to decrease, resulting in early sticking. In comparative example 2,
Although a fluorocarbon lubricant is applied to the surface of the back coat layer, it can be seen that due to sliding contact with the POM guide bottle, it is charged and the coefficient of dynamic friction increases, and a discharge phenomenon also occurs.

On the other hand, in Examples 1 and 2, in which the back coat layer held an antistatic agent, the coefficient of dynamic friction was reduced to the same level as Comparative Example 1, and sticking occurred after 100 shuttle runs. No discharge occurred, and no discharge phenomenon was observed. Particularly good results were obtained in Example 2, in which the antistatic agent was applied solely to the top layer of the back coat.

〔Effect of the invention〕

As is clear from the above description, if the present invention is applied, a magnetic recording medium in which a fluorocarbon lubricant is retained in the back coat layer can be used in sliding contact with a guide member etc. made of an organic polymer material. In this case, charging is effectively prevented by the action of the antistatic agent. Of course, since the original functions of the fluorocarbon lubricant are fully exhibited, a magnetic recording medium with excellent running properties, Flt durability, and excellent reproduction signal quality can be provided.

Claims (1)

[Claims] A magnetic recording medium in which a magnetic layer made of a metal magnetic thin film is formed on one side of a non-magnetic support, and a back coat layer holding a fluorocarbon lubricant is formed on the other side, A magnetic recording medium characterized in that the back coat layer retains an antistatic agent.