JPH0568010B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording medium with excellent running stability and durability. More specifically, the present invention relates to an excellent magnetic recording medium with improved running properties and durability by providing a robust top coat layer. Prior Art In recent years, magnetic recording media have been used for audio, video,
It has become widely used in fields such as computers and magnetic disks, and as a result, magnetic recording media have become more compact and the amount of information recorded on magnetic recording media has continued to increase. . Therefore, there is an increasing demand for improving the recording density of magnetic recording media. In order to meet the above requirements, non-binder type magnetic recording media, especially magnetic recording media whose magnetic recording layer is made of a magnetic thin film, do not contain a binder and can therefore be made thinner and thinner than coated magnetic recording media. This is advantageous because the saturation magnetization is also large. However, on the other hand, non-binder type magnetic recording media have a magnetic recording layer formed by methods such as electroplating, electroless plating, sputtering, vacuum deposition, and ion plating, and do not contain a binder.
When sliding in contact with a magnetic head, for example when recording, reproducing or erasing magnetic signals, the magnetic recording layer is scraped off or destroyed by friction caused by high-speed relative movement with the magnetic head. It was easy. In addition, in non-binder type magnetic recording media, the surface of the magnetic recording layer is easily corroded, and as the corrosion progresses, practical properties such as head touch and wear resistance tend to deteriorate, and the electromagnetic conversion properties also tend to be adversely affected. As a means of reducing the impact and friction experienced by a magnetic recording medium, there is a method of applying a lubricant to the surface of the magnetic recording layer (Japanese Patent Publication No. 39-25246). In addition, as a means of continuously supplying lubricating action to the surface of the magnetic recording layer, a lubricating layer (back coat) containing a liquid or semi-solid lubricant and an organic binder as main components is applied to the surface of the magnetic recording medium opposite to the magnetic recording layer. A method of forming a layer (Japanese Patent Publication No. 57-29769) was proposed. In this method, when the magnetic recording medium is wound into a roll, the lubricant oozed from the back coat layer on the back side transfers to the surface of the magnetic recording layer, thereby supplying the lubricant to the surface of the magnetic recording layer. This increases the durability of the magnetic recording layer (resistance to scratches and peeling), and also makes it possible to easily respond to changes in the coefficient of dynamic friction. Problems to be Solved by the Invention However, in the method described in Japanese Patent Publication No. 39-25246, the lubricant is removed by a magnetic head, etc., so the lubricating effect is not permanent, and the rust prevention and
Effects such as durability were not as expected. In addition, if a lubricant is only added to the back coat layer without forming a top coat layer on the surface of the magnetic recording layer as in the method described in Japanese Patent Publication No. 57-29769, the relationship between the surface of the magnetic recording layer and the magnetic head cannot be improved. Friction was still large, easily leading to poor running, and satisfactory results were not obtained in terms of corrosion resistance and rust prevention effects. Furthermore, if the lubricant in the back coat layer is transferred to a magnetic thin film that is not top coated, it is not noticeable, for example, when oxygen is not introduced into the deposited film (metallic film that does not contain oxygen: Japanese Patent Publication No. 57-29769). However, when oxygen is introduced (oxygen-containing metal film), which is currently the usual practice, the film becomes unstable, resulting in decreased output, clogging, no images, or insufficient frictional resistance. It was observed that the film remained large without decreasing, and sometimes the film was scraped off or destroyed. Furthermore, in contrast to the method of containing a lubricant in the back coat layer, a method of applying the lubricant to the top coat layer can be easily considered. However, although this method reduces friction, it is only temporary and does not last.
Moreover, only a magnetic recording medium with significantly inferior rust prevention, corrosion resistance, durability, etc. can be obtained. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional art, and is based on the formation of a specific top coat layer on the surface of a magnetic thin film in a magnetic recording medium having a magnetic thin film on a non-magnetic base material. By doing so, it is possible to provide an excellent magnetic recording medium that has improved running properties and durability and eliminates the above-mentioned drawbacks. Means for Solving the Problems The present invention provides a magnetic recording medium having a magnetic thin film on a non-magnetic base material, which has one or more radiation-sensitive unsaturated double bonds on the surface of the magnetic thin film and has the following formula: The present invention is a magnetic recording medium characterized by forming a top coat layer made of a compound having a group represented by: C _o F _2o+1 (wherein n is an integer between 2 and 20). The magnetic metals or magnetic alloys used in the magnetic thin film of the present invention include iron, cobalt, nickel and other magnetic metals, Fe-Co, Fe-Ni, Co-Ni,
Fe−Rh, Fe−Cu, Fe−Au, Co−Cu, Co−
Au, Co-Y, Co-La, Co-Pr, Co-Gd, Co
−Sm, Co−Pt, Ni−Cu, Fe−Co−Nd, Mn−
Mention may be made of magnetic alloys such as Bi, Mn-Sb and Mn-Al. The magnetic thin film can be applied directly or as a non-magnetic thin film layer to a known substrate such as a plastic film such as a polyester film or a polyamide film, a metal plate such as an aluminum plate, or an inorganic plate such as a glass plate. The magnetic metal or magnetic alloy can be formed by vacuum deposition, sputtering, ion plating, plating, or other methods. The magnetic thin film of the present invention can be manufactured by any of the methods mentioned above, but
As ^described in Example 5 of Publication No. 29769, a magnetic thin film (1 ), the deposition direction is tilted in the longitudinal direction (90° to 30°), which is currently common practice.
However, it is not inclined in the width direction, and while introducing O ₂ or O ₂ and Ar as an atmosphere, ~1 ×
A magnetic thin film (2) obtained by vapor deposition at 10 ^-4 Torr is preferred. This is because the vapor deposited film produced by method (1) above is entirely metallic (except for the surface that is naturally oxidized after being taken out into the air), whereas the film produced by method (2) has a trace amount of metal. When a metal or alloy is deposited in a vacuum in the presence of oxygen gas, the magnetic metal contains oxygen, and the oxygen does not form a solid solution with the metal.
Exists in oxide form. The presence of this oxide is preferable for the magnetic recording medium, and particularly when there is a large amount of oxide at the interface between the magnetic thin film and the base material and on the surface opposite to the base material, good properties are obtained in the present invention. This is because it has been found that the following can be obtained. In addition, as a method for introducing oxygen into a magnetic metal thin film, in addition to vapor deposition in the presence of oxygen as described above, a thin film obtained by vapor deposition in a vacuum without oxygen may be deposited at a temperature of, for example, 90°C and a relative humidity of 20%. It is also possible to perform forced oxidation in an atmosphere so that the surface of the deposited film consists only of oxide. The oxygen content of the magnetic thin film containing oxygen is
It is preferably in the range of 3 to 60 atomic %, calculated from the formula: (O/magnetic metal) x 100. The ferromagnetic thin film obtained as described above has one or more radiation-sensitive unsaturated double bonds on its surface and has the following formula: C _o F _2o+1 (where n is an integer between 2 and 20). A top coat layer is formed from a compound having a group represented by: Such compounds are

[ka]

【formula】

[Formula, n is an integer between 2 and 20, and m is 1
or 2). A compound having one or more radiation-sensitive unsaturated double bonds and a group represented by C _o F _2o+1 (n is an integer between 2 and 20) as used in the present invention can be prepared by a known method. It can be easily manufactured using
To give an example, a halogenated compound having a C _o F _2o+1 group, e.g. C ₃ F ₁₇ -C ₂ H ₄ I, is reacted with water to form a corresponding alcohol, e.g. C ₃ F ₁₇ -C ₂ H ₄ −
This alcohol is condensed with an unsaturated acid, e.g. acrylic acid, using a strong acid as a catalyst to form the desired compound, e.g.

[Formula] can be obtained. The above compounds alone or mixed with a lubricant,
The resulting mixture is applied to the surface of the magnetic thin film to form a top coat layer. At this time, activation energy rays may be irradiated, and the irradiation dose is preferably in the range of 0.1 to 20 Mrad. The top coat layer of the present invention has a strong adsorption force with the magnetic layer due to the use of a compound having a radiation-sensitive unsaturated double bond, thereby improving durability. Preferably, by irradiating with activation energy rays to cause a cross-linking reaction, it is quickly bonded to the magnetic layer and the durability is further improved. Further, the top coat layer of the present invention has particularly excellent running stability due to the use of a compound having a group represented by C _o F _2o+1 (n is an integer between 2 and 20). If n of C _o F _2o+1 in the radiofunctional compound is 21 or more, the binding force of the top coat layer to the magnetic thin film will be weak, and if n is less than 1, the lubricity will be significantly reduced, which is not preferable. Furthermore, the top coat layer of the present invention has radiation-sensitive unsaturated double bonds and _Co
By using a compound having both groups represented by F _2o+1 , no scratching or clogging of the head will occur. As the lubricant, it is possible to use lubricants conventionally used in this type of magnetic recording medium, such as silicone oil, fluorine oil, alcohol, fatty acid, aliphatic ester, paraffin, liquid paraffin, surfactant, etc. , fatty acids and/or fatty acid esters are preferred. Examples of fatty acids include fatty acids with 12 or more carbon atoms (RCOOH, R is an alkyl group with 11 or more carbon atoms), such as _cabryl9 , cabric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, and elaidic acid. , linoleic acid, linolenic acid, stearolic acid, etc. are preferred, and fatty acid esters include fatty acid esters consisting of a monobasic fatty acid having 4 to 20 carbon atoms and a monohydric alcohol having 2 to 20 carbon atoms; Fatty acid esters having a total of 8 to 30 carbon atoms, etc., which are composed of six or more monobasic fatty acids and a monohydric alcohol, are preferred. The silicone oil used is one made of fatty acid denatured or partially fluorinated denatured silicone oil. The alcohol used is one made of higher alcohol, and the fluorine oil used is one obtained by electrolytic substitution, telomerization, oligomerization, or the like. Furthermore, a radiation curing type lubricant can be suitably used. When using a radiation-curing lubricant, the transfer of the lubricant to the back mold is suppressed, which prevents drop-outs, reduces the difference in output depending on the inner and outer diameters when wound into a roll, and allows for online processing. There are advantages such as the possibility of manufacturing. Radiation-curable lubricants include compounds that have a molecular chain exhibiting lubricity and an acrylic double bond in their molecules, such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters. , methyl vinyl alcohol ester, allyl alcohol ester, glyceride, etc. These lubricants are represented by the structural formula: CH ₂ =CHCOOR,

[Formula] CH ₂ = CH−CH ₂ COOR, CH ₂ = CHCONHCH ₂ OCOR,

【formula】

[Formula] RCOOCH=CH ₂ , RCOOCH ₂ -CH=CH _2, etc. (where R is a straight chain or branched saturated or unsaturated hydrocarbon group, and the number of carbon atoms is 7 or more, preferably 12 or more and 23 or less) and
These can also be substituted with fluorine). Preferred specific examples of these radiation-curable lubricants include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), glycerin methacrylate (acrylate), glycol methacrylate (acrylate), silicone methacrylate (acrylate), etc. can be mentioned. The active energy rays used for crosslinking the radiation-curing additive used in the top coat layer of the present invention include electron beams using a radiation accelerator as a source, γ-rays using Co60 as a source, and β-rays using Sr90 as a source. - line,
Examples include X-rays or ultraviolet rays using an X-ray generator as a radiation source. In particular, as an irradiation source, it is advantageous to use radiation generated by a radiation accelerator from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation. In the present invention, the thickness of the top coat layer is 5 to 5.
400 Å is preferred. If it is too thick, the electrical properties may deteriorate or scratches may occur. Also, if it is too thin, clogging will occur. Since the surface roughness of a ferromagnetic thin film without a top coat is preferably 100 Å or less, it has been found that when a top coat layer is formed thereon, if it is too thick, scratches may occur. If the amount is too small, the adsorption of the top coat layer will be too weak and clogging may occur. This is the first discovery of this invention in the present invention. A particularly preferred range is 110 to 200 Å. When forming the top coat of the present invention, commonly used antioxidants, curing agents, and the like can be added in commonly used amounts. When a curing agent is used in the present invention, radiation-curable monomers and oligomers are suitable as the curing agent. Molecular weight for radiation-curable monomers
Compounds with a molecular weight of less than 2000 as oligomers
2,000 to 110,000 are used. These are styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate,
Dimethylene glycol dimethacrylate, 1,6
-Hexane glycol diacrylate, 1,6-
including hexane glycol dimethacrylate, and particularly preferably including: N-vinylpyrrolidone, pentaerythritol tetraacrylate (methacrylate), pentaerythritol triacrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane Diacrylate (methacrylate), polyfunctional oligoester acrylate (Aronix M-7100, M manufactured by Toagosei Co., Ltd.)
-5400, 5500, 5700, etc.) Acrylic modified products of urethane elastomers (Nitsuporan 4040), or those into which functional groups such as COOH have been introduced, acrylates (methacrylates) of phenol ethylene oxide adducts, and Compounds with an acrylic group (methacrylic group) or ε-caprolactone-acrylic group attached to the pentaerythritol condensed ring:

[Chemical formula] and special acrylates represented by the following general formula: (CH ₂ =CHCOOCH ₂ ) ₃ −CCH ₂ OH; (CH ₂ =CHCOOCH ₂ ) ₃ −CCH ₂ CH ₃ ; [CH ₂ =CHCO(OC ₃ H ₆ ) _o −OCH ₂ 〕 ₃ −
CCH ₂ CH ₃ ; (n≒3)

[ka]

[ka]

[ka]

[Case] (n≒16) CH ₂ CHCOO− (CH ₂ CH ₂ O) ₄ −COCH=CH ₂ ;

[ka]

[ka]

[Chemical] A: acrylic acid; Examples include those into which functional groups such as COOH have been introduced:

[Chemical formula: R ₁ , R ₂ : alkyl group, n: integer] In the present invention, when a lubricant, antioxidant, curing agent, etc. are added to the top coat layer, the total weight of these It is preferable that the amount is within 10 times the weight of the compound having one or more double bonds and a group represented by C _o F _2o+1 (n is an integer between 2 and 20). . Further, it is preferable that the weight of the antioxidant does not exceed the weight of the lubricant+curing agent. Although it is not particularly necessary to form a back coat layer in the magnetic recording medium of the present invention, running properties are further stabilized by forming a back coat layer.
The back coat layer can be formed using commonly used inorganic pigments, lubricants, and organic binders. Hereinafter, the present invention will be explained in more detail with reference to Examples. The parts shown below are by weight. The tests shown in the following Examples and Comparative Examples were conducted in accordance with the following method: 1. Still characteristics Record at 5MHz and measure the still characteristics of the reproduced output. 10 minutes or more is considered an OK level. 2 Measurement of friction on the magnetic side Wrap the magnetic tape so that the magnetic side faces the cylinder, apply a load of 20g to one end, and measure the friction by reading the change in tension when the cylinder is rotated 90 degrees. 3 Output S/ when recording and playing back at a center frequency of 5MHz
Shows the N ratio (relative value). Modify a VHS VCR
Allows measurement up to 5MHz. 4 Rust Store in an environment of 50℃ and 90% relative humidity for 2 days. 5 Envelope, head clogging, and repeated running were measured using a Matsushita VHS deck (AG2200). 6. Top coat fraying was measured by observing the tape after repeated running with an optical microscope at 400x magnification. Formation of ferromagnetic thin film A polyester film with a thickness of 12 μm is moved along the circumferential surface of a cylindrical cooling can, and O ₂ + Ar (volume ratio 1:1) is flowed at a rate of 800 c.c. per minute to create a vacuum. of
Co80 in a chamber with 1.0×10 ^-4 Torr,
An alloy made of Ni20 was melted and deposited obliquely only at the incident angle of 90° to 30° to form a Co--Ni--O thin film with a thickness of 0.15 μm. A large amount of oxygen was unevenly distributed at the interface with the base and on the surface opposite to the base. Furthermore, the surface opposite to the base was covered almost exclusively with oxide. The average amount of oxygen in the Hc=1000Oeo film was 40% in terms of atomic ratio to Co and Ni (O/CoNi×100). Example 1 The following composition: parts

[Chemical] 1 Stearyl acrylate 0.5 MEK 100 was stirred and mixed at room temperature for 1 hour, and the resulting mixture was applied to the surface of the above magnetic thin film with a gravure cylinder to a uniform thickness. After drying at 100℃ for 1 minute, Electron beam irradiation was performed in N ₂ gas at 150 KeV, 6 mA, and 3 Mrad to form a top coat layer with a thickness of 20 Å. Regarding the magnetic recording medium thus obtained, steel properties, magnetic surface side friction, output, rust occurrence, envelope, repeated running, head clogging, and top coat scratching were measured. The results obtained are shown in the table below. Example 2 The following composition: parts

[Formula] 0.5 Dodecyl palmitate 1.0 A top coat layer was formed in the same manner as in Example 1 using MEK 100. The same measurements as in Example 1 were carried out, and the obtained results are shown in the table. Comparative Example 1 A top coat layer was formed in the same _manner as in Example 1 using _the following composition: C3F17 _{- C2H4} -COOH1MEK100. The same measurements as in Example 1 were carried out, and the obtained results are shown in the table. Comparative Example 2 A top coat layer was formed in the same manner as in Example 1 using the following composition: (2-hydroxyethyl) methacrylate-acid phosphate 0.7 behenic acid 0.5 MEK 100. The same measurements as in Example 1 were carried out, and the obtained results are shown in the table. Comparative Example 3 The same measurements as in Example 1 were carried out without forming a top coat layer on the above magnetic thin film. The results obtained are shown in the table.

【table】

[Table] Effects of the invention According to the present invention, the running stability and durability are excellent;
A magnetic recording medium with less dropout and excellent rust prevention properties can be obtained. Further, in the present invention, the frictional resistance can be further reduced by including a lubricant in the top coat layer. The magnetic recording medium of the present invention, which has excellent various properties as described above, can be used as audio tape, video tape, computer tape, endless tape, magnetic disk, etc. Among them, dropout is one of the most important properties. tape,
It can be used as a computer tape and is very useful. In recent years, the specific top coat layer of the present invention has been applied to high-bias HiFi audio cassette tapes, video cassette tapes, master tapes for videotape contact transfer printing, etc., which have undergone remarkable technological progress and whose marketability is expanding. By using a magnetic recording medium made of a thin metal film, it is possible to obtain a high-performance tape with extremely good electromagnetic conversion characteristics and physical reliability, and the magnetic recording medium of the present invention is said to be highly useful and excellent. be able to.

Claims (1)

[Claims] 1. A metal magnetic thin film is provided on a non-magnetic base material, and on the surface of the magnetic thin film, [formula] and [formula] (in the above formula, n is between 2 and 20) is an integer, m is 1
A magnetic recording medium comprising a top coat layer made of a radiation-sensitive compound selected from at least one of the compounds represented by (1) or (2).