JPS60187921A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent resistance to wear and corrosion with low frictionability without decreasing the electromagnetic conversion characteristic thereof by providing a lubricative coating layer consisting of a fluorine graft polymer on the front of a thin ferromagnetic metallic film provided on a substrate and the rear of the substrate. CONSTITUTION:A thin ferromagnetic metallic film is formed on a substrate consisting of a polymer film, glass plate, etc. and thereafter a lubricative coating layer contg. a fluorine graft polymer, more particularly preferably a single graft polymer having the branch of polymethyl methacrylate in the backbone component of the copolymer of the oligomer expressed by the formula and fluoroalkyl acrylate, etc. expressed by CF3-(CH2)n-CH2CH2OCOCH=CH2 (where, n=2- 14) or said polymer together with a surface treating agent having compatibility with the compatible component of said polymer, for example, a polymer, etc. of (meth)acrylic acid or the ester thereof is formed on the front surface of the thin magnetic film and the rear surface of the substrate. The wear resistant and lubricative layer having excellent adhesion is thus formed on the front surface of the magnetic layer and the surface of the substrate by which the recording medium having excellent durability and runnability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface comprising a ferromagnetic metal thin film provided on a substrate by vacuum evaporation, ion blasting, sputtering, plating, etc. and/or a lubricating coating layer formed on the back surface of the substrate. The present invention relates to a modified magnetic recording medium.

The purpose is to improve the running stability, durability, and corrosion resistance of magnetic recording media that use ferromagnetic metal thin films as recording media.

In recent years, instead of magnetic recording media made by coating and drying ferromagnetic metal powder together with a binder on a substrate, a magnetic layer of a thin ferromagnetic metal film, which has excellent high-density magnetic recording properties, has been deposited on the substrate. 2. Description of the Related Art Magnetic recording media deposited by sputtering or the like have been attracting particular attention as recording memories for audio recording, video recording, 8% video recording tapes, perpendicular recording, optical disks, and the like.

However, this metal magnetic layer is easily corroded by oxygen, moisture, etc. in the air, and is also easily worn out by running in contact with magnetic fields, drums, posts, etc.

Therefore, it is necessary to improve the corrosion resistance and abrasion resistance of the surface of the tape without reducing the electromagnetic conversion characteristics, as well as to have low abrasion properties, a thin and uniform thickness, and strong adhesion and flatness. Much research and development has been conducted on lubricating surface treatment agents and treatment methods that can achieve this.

One of the conventionally proposed methods is to alloy the surface of the metal thin film itself, or to evaporate or sputter a film of metal or inorganic oxide such as magnesium, aluminum, platinum, palladium, chromium, titanium, or Sin on the surface. A method has been proposed in which the nuclide is formed using a coating having high hardness and corrosion resistance. Although this method is effective in improving corrosion resistance and abrasion resistance, the adhesion strength is insufficient, and on the other hand, the high hardness causes problems such as rapid destruction of the recording medium and transducer, as well as complicated problems. There is a problem in that it requires processing and is costly.
No satisfactory results have been obtained. In addition, treatment agents such as waxes, fatty acids/fatty acid esters, fatty acid amides, and fluorine surfactants can be chemically adsorbed to improve surface lubricity by utilizing adsorption with the metal thin film surface, and silicone oils and A method of applying a treatment agent such as fluorine oil has also been proposed. This method reduces friction against the magnetic head etc. and temporarily improves durability, but
As the treatment agent is used, it evaporates or is scraped off, making it difficult to maintain its effects for a long time.

Another method is to coat the surface of the magnetic layer or the back surface of the substrate with a urethane resin such as tetrafluoroethylene telomer,
silicone resin, fluororesin, epoxy resin or radiation,
Many proposals have been made to coat with polymeric substances such as ultraviolet curable resins. This has a temporary effect on low abrasion, corrosion resistance, and durability, but considering that it causes a decrease in electromagnetic conversion characteristics called spacing loss, it is desirable that the polymer material coating is at most 500A. is 20
It must have a film thickness of about 0A and uniform and smooth flatness. However, with such a film thickness, it is difficult to completely prevent moisture from entering, and there are problems in terms of wear resistance and chemical resistance. Furthermore, it is difficult to form a uniform thin film with little output fluctuation by surface treatment by coating a known polymeric substance.

Also, the back side of the base is strongly required to have wear resistance and lubricity in order to prevent tape squeal, improve running stability, and durability. It has been proposed to provide a back coat layer by forming a polymer layer containing a lubricant. However, in any case, according to the prior art, a product that is satisfactory as a protective layer for a ferromagnetic metal thin film or as a backside treatment agent for a substrate has not yet been obtained. The present inventors have arrived at the present invention as a result of intensive research aimed at overcoming the drawbacks of conventionally proposed known methods.

It is an object of the present invention to solve the above-mentioned drawbacks of the prior art, and to provide a magnetic layer on the surface of a magnetic layer of a ferromagnetic metal thin film provided on a substrate by vacuum evaporation, ion blasting, sputtering, plating, etc. and/or on the back surface of the substrate. Another object of the present invention is to provide a magnetic recording medium provided with a uniform protective film having low friction and excellent wear resistance and corrosion resistance without deteriorating electromagnetic conversion characteristics.

An example of the magnetic recording medium according to the present invention is a polyethylene terephthalate film (hereinafter referred to as PE'l' film).
, polyimide film or polyamide film, etc., or polycarbonate plate, acrylic.

Magnetic metals such as Fe, Co, Ni, Cr, Ga, Ge, or After providing a ferromagnetic metal thin film of an alloy containing these as a main component as a magnetic layer, a fluorine-based graft polymer alone or in combination with another surface treatment agent is used on the surface and/or the back surface of the substrate.
It is equipped with a farm protection membrane.

In the present invention, after providing the magnetic layer, in order to improve the durability and adhesion of the magnetic layer, a polymer compound or an inorganic compound (S
A base layer may be formed by performing a base treatment such as formation of a magnetic material (iO□, etc.) and alloying of the magnetic material itself, and then a lubricating coating layer may be formed.

According to the present invention, a top coat layer having excellent wear resistance, lubricity, corrosion resistance of the magnetic layer, and adhesion to the magnetic layer can be formed on the surface of the magnetic layer, and a top coat layer having excellent wear resistance, lubricity, and adhesion to the magnetic layer can be formed on the back surface of the substrate. A back coat layer with excellent adhesion to the substrate can be formed. The protective film formed in this way has no adverse effect on the magnetic layer,
Since the magnetic recording medium does not deteriorate electromagnetic conversion characteristics and has low friction and excellent corrosion resistance, wear resistance, etc., a magnetic recording medium with excellent running stability and durability is provided.

The fluorine-based graft polymer used in the present invention is preferably one manufactured using at least one raw material component of a macromonomer, that is, an oligomer having a polymerizable functional group at one end of the molecular chain.

Examples of the terminal polymerizable functional group of this oligomer include acryloyloxy, methacryloyloxy, allyloxy,
Examples include vinyl polymerization types such as styryl, and polycondensation polymerization types such as dicarboxy and dihydroxy.
Monomers constituting the oligomer can be selected as appropriate depending on the purpose, and include, for example, alkyl acrylate, alkyl methacrylate, styrene, polyethylene glycol methacrylate, dimethylsiloxane, fluoroalkyl acrylate, and the like. This oligomer is obtained by radical polymerizing, for example, methyl methacrylate in the coexistence of thioglycolic acid, and has a molecular weight of 1.000 to i0. It is an oligomer having a methacrylic acid ester type terminal group obtained by obtaining a one-terminated carboxylic acid prepolymer of ooo and reacting this with glycidyl methacrylate.

For this oligomer, for example, fluoroalkyl acrylate (CFs + CFt) n CHtC1 (20CO
If CH=CH, a mixture of n-4 to 12) is used, a fluorine-based graft polymer having a fluorine component as the trunk and polymethyl methacrylate as the branches can be obtained. The content of fluoroalkyl acrylate units in this fluorine-based graft polymer is preferably 5 to 90% by weight, and 10 to 40% by weight.
is even more preferable. Fluorine-based graft polymers with a content of less than 5% by weight of fluoroalkyl acrylate units do not exhibit sufficient performance in terms of friction properties, corrosion resistance, etc., and when the content exceeds 90% by weight, fluorine-based graft polymers are susceptible to solvent infiltration. Solubility tends to deteriorate, and the modification effect by fluorine cannot be improved.

According to the present invention, even when used alone, this fluorine-based graft polymer improves adhesion, low friction, wear resistance, corrosion resistance, etc. on the surface of the magnetic layer, and also improves the properties on the back surface of the substrate.
It also forms a similar excellent coating layer and can fully achieve the intended purpose.

In this case, the fluorine-based graft polymer should preferably have excellent film-forming properties and be compatible with the magnetic layer, and for this purpose, it is best to use a graft polymer that has functional groups such as carboxyl groups and hydroxyl groups. For example, by copolymerizing a methacrylic acid ester type macromonomer, a fluoroalkyl acrylate, acrylic acid and/or methacrylic acid (hereinafter referred to as (meth)acrylic acid), or an alkyl ester thereof, hydroxylte/L/(meth)acrylate, etc. It is preferable to use the obtained fluorine-based graft polymer.
The desired purpose can be achieved with excellent results by adding and dissolving the fluorine-based graft polymer dissolved in a surface treatment agent, which will be described in detail later, and coating the surface of the magnetic layer or the back surface of the substrate with this fluorine-based graft polymer-dissolved surface treatment agent. Depending on the purpose and use, it may be better than using it alone. This is because the fluorine-based graft polymer has extremely excellent surface migration ability, so if it is added to a surface treatment agent and formed into a film in a normal environment, that is, in air or in an inert gas such as nitrogen, it will not migrate to the surface of the coating film. This is because the fluorine-based graft polymer migrates and concentrates, making it easy to modify the surface of a coating film. In addition, since the fluorine-based graft polymer is composed of a fluorine component and a branch component that is compatible with the surface treatment agent polymer, the fluorine-based graft polymer that has migrated to and concentrated on the coating film surface, due to the anchoring effect of the compatible components, It does not easily fall off from the coating surface and has excellent long-lasting modification effects. Furthermore, because it contains the y-element component, the film has many advantages such as low friction, water lifting properties, oil repellency, and no moisture permeability, so it has excellent corrosion resistance. There is.

Therefore, a coating layer that can fully achieve the object of the present invention can be obtained.

In the present invention, when a surface treatment agent in which the fluorine-based graft polymer is dissolved is used for the top coat or back coat, the surface treatment agent that can be used includes a component that dissolves the fluorine-based graft polymer and is compatible with the fluorine-based graft polymer. Preferably, a surface treatment agent is compatible with ℃・.

The surface treatment agent is composed of a polymer or a polymer and a solvent. Examples of polymers include polypolymers of α, β-ethylenically unsaturated monomers, α4β-ethylenically unsaturated carboxylic acids and derivatives thereof, polymers produced by polycondensation reactions, polymers produced by polyaddition reactions, etc. In addition to being able to use the polymer itself, a curable composition comprising a radically polymerizable component can also be used as a polymer precursor. Specific examples of polymers include styrene, acrylonitrile, vinyl chloride, etc. as α,β-ethylenically unsaturated monomers, and (meth)acrylic acid, maleic acid as α,β-ethylenically unsaturated carboxylic acids. Examples include monovalent and divalent carboxylic acids such as. Derivatives of α,β-ethylenically unsaturated carboxylic acids include alkyl esters of (meth)acrylic acid, such as esters of ethyl, butyl, 2-ethylhexyl, etc., and hydroxyalkyl esters of acrylic acid or methacrylic acid. can include (meth)acrylic acid hydroxyethyl ester, hydroxypropyl ester, etc. Examples of surface treatment agents include air-drying lacquers and baking-type clear enamels obtained by polymerizing a combination of these monomers.

Examples of the polymer obtained by the polycondensation reaction include linear polyester resins, alkyd resins, polyamide resins, epoxy resins, etc. obtained by ordinary polycondensation reactions. Examples of polymers produced by polyaddition reactions include polyurethane resins and polyurea resins obtained by ordinary polyaddition reactions. Other examples include silicone resins and fluororesin coating agents.

Furthermore, cellulose derivatives such as ethyl cellulose, butyl cellulose, nitrocellulose, etc. can also be used in combination with these polymers. When using a curable composition consisting of a radically polymerizable component as a polymer precursor, heat polymerization curing using a radical polymerization initiator or redox curing at around room temperature by using a radical polymerization initiator and a polymerization curing accelerator together is possible. There are various curing methods such as polymerization curing, ultraviolet curing using a photopolymerization initiator, and electron beam curing that may or may not use a photopolymerization initiator, and compositions that can be polymerized and cured by such methods. You can use either one. Specifically, as a radically polymerizable component, (meth)
Examples include acrylic acid ester monomers, unsaturated polyesters, polyester (meth)acrylates, urethane (meth)acrylates, epoxy (meth)acrylates, polyamide (meth)acrylates, and thiol/ene-based polymers.

The amount of fluorine-based graft polymer added to the surface treatment side is:
It is preferably 0.01 weight or more based on the polymer or radically polymerizable component of the surface treatment agent. If the amount added is less than 0.01% by weight, the intended effect cannot be sufficiently exerted on the surface of the coating film.

Although these surface treating agents can be used either dissolved in an organic solvent or not dissolved in an organic solvent, it is generally preferable to use them as organic solvent type surface treating agents. It increases the solubility of the fluorine-based graft polymer, increases the migration of the fluorine-based graft polymer to the coating surface, and improves the orientation of the fluorine component to the surface, making it possible to form a thin film that does not adversely affect electromagnetic conversion characteristics. This is because a uniform smooth surface can be obtained due to the reduction in viscosity.

Usable solvents include hydrocarbon solvents such as toluene, xylene, and cyclohexane, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, methyl cellosolve, and ethyl cellosolve. Among these various solvents, one or a mixed solvent of two or more is preferably used. Also, depending on the method used to apply the treatment agent, antistatic agents,
Additional amounts of body pigments, waxes, leveling agents, etc. may be added.

The above-mentioned fluorine-based graft polymer alone or in combination with the above-mentioned various processing agents has a lubricating property and is applied onto substrates such as various plastics and glass by vacuum deposition, ion blasting, sputtering, plating, etc. It is coated on the front and back sides of various recording media such as tapes, perpendicular recording and magneto-optical disks made of thin ferromagnetic metal films, or the back side of the substrate. Coating, gravure offset, slit reverse coating, spray coating, spinner coating, ticking coating, curtain flow coating, etc. on the surface, drying, and then removing depending on the processing agent used and optionally crosslinking with incyanate resin. Or, if a radically polymerizable composition is used, it can be polymerized and cured by heat, ultraviolet rays, or electron beams to form a strong coating, forming a smooth film with a thickness of several tens of Å or more on the surface of the magnetic layer and/or the back surface of the substrate. It is possible to form a coating layer that meets the desired purpose, and it is possible to achieve excellent effects that have not been achieved before.

Next, the present invention will be explained with reference to Examples and Comparative Examples, but these are only some of the many experiments and should not be limited to these. Incidentally, "part" on each side represents part by weight, "chi" represents weight %, and the coefficient of friction during running of the vapor-deposited tape was determined by the following formula.

To: Intention speed: 14.2 mtp7 reference example 1 In a glass flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and gas inlet, 10 parts of methyl methacrylate (hereinafter abbreviated as MMA) and acetone ( 1
7,5L)-) 06 parts of a toluene mixed solvent was charged, and after N1 was introduced, 0.5 parts of azobisisobutyronitrile (hereinafter abbreviated as AIBN) as a polymerization initiator and thioglycolic acid as a chain transfer agent were added under reflux. 0.32 part was added to initiate polymerization. Over the next 4.5 hours, 90 parts of MMA was continuously added dropwise, and 2.08 parts of thioglyfuric acid was dissolved in 7 parts of toluene and added in 9 portions every 30 minutes. Polymerization was carried out by adding 1.5 parts in 3 portions every 1.5 hours. Thereafter, the mixture was refluxed for 2 hours to complete the polymerization, and a polymer solution having the following structural formula CI) was obtained.

The reaction temperature was 77-87°C equivalent/9.

Cl-13 Next, after distilling off part of the acetone from the reaction solution, 0.5% of triethylamine was added as a catalyst, and 200 ppm of hydroquinone monomethyl ether was added as a polymerization inhibitor.
was added, and 1.2 times the molar amount of glycidyl methacrylate based on the acid value was added, followed by reaction under reflux (approximately 110°C) for 11 hours. The acid value was reduced by drying under reduced pressure at °C to obtain 90 parts of a macromonomer having the following structural formula [I[). The polystyrene equivalent molecular weight determined by gel permeation chromatography (hereinafter referred to as GPC) was 2,040 (number average) and &470 (weight average). Also, the hydroxyl value is 0.
350") - 19/19.

Cl-1゜ CHl-OCO-C-CI.

Reference Example 2 Synthesis of fluorine-based graft polymer by macromonomer method Synthesis of fluoroalkyl acrylate (trunk)/methyl methacrylate (branch)-comb-shaped graft polymer Macromonomer 70 obtained in Reference Example 1 was placed in the same apparatus as Reference Example 1. and a fluoro moiety having the following structural formula [l11] were charged, N was introduced, and the mixture was allowed to react under reflux (about 100° C.) for 5 hours.

(1) CF, +CFt+CH2-CH2-0CO-C
H = CI (mixture of n = 4 to 12 in 2, (average value of n approximately 7) This reaction solution was poured into 10 times the amount of methanol to precipitate, and 80
The mixture was dried under reduced pressure at °C to obtain 67 parts of a graft polymer.

This product showed a single peak by GPC, and the polystyrene equivalent molecular weight was 10,800 (number average) and 21.
700 (weight average).

In addition, trifluorotoluene was added as an internal standard substance, and the H-NMR spectrum was measured using CDC4 as a solvent. The content of the graft polymer I4y) MMA unit was calculated from the area ratio.
It was 60 inches.

Therefore, the content of fluoroalkyl acrylate units was 40%.

Reference Example 3 Synthesis was carried out in the same manner as in Reference Example 1 using the same apparatus and the same operation using the macromonomer method, but the amount of fluoroalkyl acrylate was reduced and fluoroalkyl 7,
Acrylate unit content is 31 inches, molecular weight is approximately 12,00
A fluorine-based graft polymer of 0 (number average) was obtained.

Example 1.2 and Comparative Examples 1 to 4 A magnetic layer of a ferromagnetic alloy thin film consisting of 80% C0-20% Ni was formed on a 12 μ thick PET film by vacuum evaporation while forcibly introducing oxygen gas. A vapor-deposited tape was obtained.

A processing agent having the composition shown below was applied to the surface of this vapor-deposited tape or the back surface of the substrate by a slit reverse coating method or a gravure coating method, and was cured by drying with hot air and irradiating with ultraviolet rays. A film with a thickness of about 20 OA was formed on the surface of the magnetic layer, and a film with a thickness of 1 μm was formed on the back surface in both Examples and Comparative Examples.

Table 1 and FIGS. 1 and 2 show the measurement results of each characteristic for the front side of the magnetic layer and the back side of the substrate.

Example 1 The Fluorine cord-based graft potrimer obtained in Reference Example 2 was mixed with luene/M EK = 1/1 (weight ratio)
The coating was applied at a concentration of 5% by weight based on a mixed solvent of 1 by the slit reverse coating method, and dried with hot air at 90° C. for 3 minutes.

Example 2 A composition in which 30 g of the fluorine-based graft polymer obtained in Reference Example 1 was added to the above resin composition was added to a mixed bath of toluene/ethyl acetate/MEK=2/1/2 (weight ratio). 5 Q in the agent, apply this, and use 3 high-pressure water lamps (concentrating type, 80 W/cIn) made by Iwasaki Electric Co., Ltd.
Cured at a speed of m/m.

After treating the back side of the substrate in Example 1.2 above, the composition was mixed with toluene/ethyl acetate/MEK=2/1/2.
A solution containing 15% of the mixed solvent (weight ratio) was applied using a 200 mesh gravure plate, and 50 m/m was applied using three high-pressure mercury lamps (concentrating type, 80 W/cm).
It was cured by UV irradiation at a speed of .

Comparative Example 1 A 5% ethanol solution of a perfluoroalkyl ethylene oxide adduct (70 Lard FC-430 manufactured by Sumitomo 3M ■) was applied to the surface of the vapor-deposited tape obtained above by slit reverse coating, and the mixture was heated at 90°C for 60 minutes. A drying process was performed for a minute.

Comparative Example 2 The surface of the magnetic layer was washed with polyvinyl potassium sulfate (washed with Wako pure water, then blown with dry air, the washing water was removed,
Dry with hot air at °C.

Comparative Example 6 A titanium film was formed on the surface of the magnetic layer to a thickness of 20 OA by vacuum deposition.

Comparative Example 4 A sample was formed in the same manner as in Example 2 except for using the fluorine-based graft polymer in Example 2 and adding 6 parts of a fatty acid ester (Kemar PL-002 manufactured by Riken Vitamin ■) as a new lubricant.

As the back surface treatment in Comparative Examples 1 to 4, cellulose derivative ( Ys) 77- Kotak C
AB551-001) A composition containing 5 parts of wax, 6 parts of PE wax, and 2 parts of fatty acid amide was made into a 15% solution of a mixed solvent of toluene/MEK = 1/1 (weight ratio), and applied by gravure coating. It was dried with hot air at 90°C for 6 minutes.

From the above results, it was possible to obtain a magnetic recording medium obtained using the fluorine-based graft polymer of the present invention with excellent low friction, wear resistance, and repellency without deteriorating the electromagnetic conversion characteristics. . Furthermore, it was possible to obtain an excellent recording medium which was free from scratches caused by reels, knobs, etc. on the back side of the substrate, and which did not cause dew condensation or blocking.

Example 3 Te was vacuum-deposited on a glass plate to a thickness of 30 OA, and the following composition was applied to the surface of the glass plate: ethyl acetate/MIBK/ethanol/fluorine inert liquid (product name Fluorinert 77, manufactured by 3M) = 35/35 /15/15 (weight ratio) in a mixed solvent at a concentration of 10% by spinner coating, and then cured by UV irradiation for 30 seconds using a water-cooled high-pressure mercury lamp (JetLy JL-4300 manufactured by Oak Seisakusho) to 200A. A thick protective film was formed. The R/W characteristics of this optical recording material were exactly the same as those without the protective film, did not change even after the durability test, and the reproduction output was also the same, providing an excellent effect. Further, it may be formed between the surface of the recording material and the protective layer or on the protective layer by vacuum deposition to a thickness of 5i022μ, which can further improve the effect.

Example 4 The fluorine-based graft polymer obtained in Reference Example 2 was added to a 50 μm PET film substrate with surface properties in toluene/Ml;
5 in a mixed solvent of /fluorocarbon rubent (Fluorinert 77 manufactured by 3M) = 1/1/1 (weight ratio)
-, and a protective film with a thickness of about 100λ was formed by a spin code method.

As a result, a lubricating layer with excellent wear resistance and a friction coefficient μ of 0.08 and a scratch strength of 180 g could be obtained.

Furthermore, a perpendicular recording medium with good corrosion resistance without reducing the S/N ratio due to the water vapor permeability characteristic of fluorine-based materials was obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between running time and friction coefficient for the vapor-deposited tape obtained in Example 2, and FIG. 2 is a diagram showing the relationship between running time and friction coefficient for the vapor-deposited tape obtained in Comparative Example 4. FIG. 't''0・・・Intensity 1゛、・・・・・・Outtension Patent Applicant Toagosei Chemical Co., Ltd. Olympus Optical Co., Ltd. ) ft-Gyochi Iji (Continued from page 1) Inventor: Fumi Kojima Department, Funami-cho Company Research Institute, Minato-ku, Nagoya City 0 Inventor: Hiroshi Kato 1, Funami-cho Company Research Institute, Minato-ku, Nagoya City 1-chome Toagosei Chemical Co., Ltd. 1-1 Toagosei Chemical Co., Ltd.

Claims (1)

[Claims] A magnetic recording medium in which a lubricating coating layer made of a fluorine-based graft polymer is formed on the surface of a magnetic layer made of a ferromagnetic metal thin film provided on a substrate and/or on the back surface of the substrate.