JPH061545B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium having a magnetic layer on a non-magnetic support, such as a magnetic tape or a magnetic disk. More specifically, the present invention relates to The present invention relates to an improvement of a lubricant for improving the runnability of some magnetic recording media.

[Outline of Invention]

The present invention, in a magnetic recording medium having a magnetic layer formed on a non-magnetic support, retains a higher fatty acid ester of polyglycerin as a lubricant, thereby significantly reducing the friction coefficient. This is intended to improve the running performance.

[Conventional technology]

A magnetic recording medium such as a magnetic tape or a magnetic disk travels while in contact with a guide member or the like, and therefore it is required to have a small friction coefficient and excellent running stability. Since it is in strong sliding contact, it is required to have excellent wear resistance.

Therefore, in order to improve the running property and wear resistance of the above-mentioned magnetic recording medium, methods such as previously mixing a lubricant in the magnetic layer in advance or forming a lubricant layer on the surface of the magnetic layer have been tried. ing. In this case, as the lubricant, solid lubricants such as molybdenum disulfide, graphite and wax, higher fatty acids, esters composed of these higher fatty acids and monohydric alcohols, silicone oils, or JP-A-56-1119931 are disclosed. It has been proposed to use monoglycerides and the like as described.

However, according to the experiments conducted by the present inventor, it has been found that the above-mentioned respective lubricants cannot be said to have a sufficient lubricating effect, and the fluctuation of the frictional force is large.

Alternatively, it has been found that the addition of these lubricants tends to impair the performance of the magnetic recording medium in some cases. For example, the solid lubricant is not very effective in improving the durability, and if added in a large amount, the magnetic properties may be deteriorated. Further, when a fatty acid or the like is used as a lubricant, it is difficult to impart sufficient lubricity over a long period of time, and running deterioration due to aging, blooming particularly when mixed in the magnetic layer, sticking phenomenon to a tape, Problems such as stick-slip occur.

[Problems to be solved by the invention]

As described above, the conventionally known lubricant cannot provide a sufficient lubrication effect and runnability, and further improvement is desired.

Therefore, the present invention provides a lubricant capable of imparting good running properties without deteriorating the durability and magnetic characteristics of the magnetic recording medium, and provides a magnetic recording medium having a small friction coefficient and excellent running properties. The purpose is to do.

[Means for solving problems]

The present inventors have conducted extensive studies on various lubricants that do not achieve the above-mentioned objects, and have found that higher fatty acid ester of polyglycerin is suitable as a lubricant meeting the above-mentioned objects, and completed the present invention. It is a thing.

That is, the present invention provides a magnetic recording medium having a magnetic layer formed on a non-magnetic support, the magnetic recording medium having the general formula (However, n represents an integer of 3 or more.) It is characterized by holding a higher fatty acid ester of polyglycerin.

The higher fatty acid ester of polyglycerin is obtained by an esterification reaction between polyglycerin and a higher fatty acid, as shown in the following formula.

(However, in the formula, R represents a hydrocarbon group having 5 to 21 carbon atoms.) In addition, in the above formula, although it is described for convenience that the esterified portions are sequentially and regularly arranged. The position of the hydroxyl group esterified with the higher fatty acid may be a side chain or an end of the hydroxyl group of polyglycerin.

Moreover, monoesters, diesters, triesters, tetraesters, pentaesters, etc. can be obtained depending on the number m of the higher fatty acid to be reacted. Among these, the higher fatty acid ester of polyglycerin used as a lubricant in the present invention is Either may be used. Therefore,
In the above formula, m = 1 to n + 2 may be set. In particular,
When m = n + 2, the above reaction formula is as follows.

(In the formula, R is the same as the above-mentioned group.) Incidentally, these higher fatty acid esters of polyglycerin are
The monoesters, diesters, triesters, tetraesters, pentaesters, etc. as described above may be simple substances, but are usually a mixture of these and correspond to monoesters or diesters depending on the residual hydroxyl value. , Equivalent to triester, equivalent to tetraester.
In addition, according to the experiments of the present inventor, it has been found that it is particularly effective for reducing the friction coefficient that some of the hydroxyl groups of polyglycerin remain in the molecule without being esterified.

On the other hand, examples of the higher fatty acid used in the esterification reaction include a saturated fatty acid having 5 to 21 carbon atoms or an unsaturated fatty acid, and the hydrocarbon group thereof may be linear or branched. For example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Examples thereof include saturated fatty acids such as stearic acid and unsaturated fatty acids such as oleic acid, elaidic acid, linoleic acid and linolenic acid.

When the polyglycerin higher fatty acid ester used in the present invention is contained in the magnetic layer, it is preferably 0.2 to 4 parts by weight with respect to 100 parts by weight of the magnetic powder in the magnetic layer. Further, as will be described later, when it is contained in the back coat layer on the back surface of the non-magnetic support, it is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder in the back coat layer. Further, as described below, when a top coat layer or a coating layer made of the above lubricant is formed by coating, the coating amount of the lubricant is 1 to 1000 mg / m ²
Is desirable.

Next, the structure of the magnetic recording medium according to the present invention, for example, a magnetic tape is shown in FIGS.

FIG. 1 shows a magnetic layer (2) containing the above lubricant formed on the surface of a non-magnetic support (1). The same applies to the following drawings, but the layer containing the lubricant shows a dotted cross section in the drawings.

FIG. 2 shows a state in which the top coat layer (3) made of the above lubricant is formed on the surface of the magnetic layer (2). FIG. 3 shows a state in which the coating layer (4) made of the above lubricant is formed on the back surface of the non-magnetic support (1). FIG. 4 shows the back coat layer (5) formed on the back surface of the non-magnetic support (1) containing the above lubricant, and FIG. 5 shows the back coat layer (5) on the back coat layer (5). The state in which the coating layer (6) made of the above lubricant is formed is shown in FIG. The back coat layer (5) is provided for various purposes, but this is for the purpose of stabilizing the running property by appropriately controlling the surface roughness of the back surface or for the purpose of preventing electrification. For this reason, the back coat layer may be formed by coating a mixture of carbon black in a binder, or by further mixing a non-magnetic pigment such as α-Fe ₂ O ₃ , alumina, talc and the like. The present invention can be applied not only to such a magnetic tape, but also to a magnetic disk having a magnetic layer on the front surface or the front and back surfaces. Further, the position for holding the lubricant is not limited to each of the above-mentioned examples, and can be set in the magnetic layer and on the front surface and / or the back surface of the magnetic layer.

Further, when the top coat layer or the coating layer made of the above-mentioned lubricant is applied and formed, it is preferable to dissolve it in some solvent and apply it. In this case, the solvent used is a low solvent such as Freon, hexane, ethanol or the like. A solvent having a boiling point may be used.

By the way, as the ferromagnetic powder used in the magnetic layer, any ordinary powder can be used. Therefore, examples of the ferromagnetic powder that can be used include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, and iron nitride.

When the ferromagnetic iron oxide particles are represented by the general formula FeOx, those having an X value in the range of 1.33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1. 5
0), magnetite (Fe ₃ O ₄ , X = 1.33) and their solid solutions (FeOx, 1.33 <X <1.50)
Is. Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing iron oxide is roughly classified into two types: a doped type and an adhered type.

Examples of the ferromagnetic chromium dioxide include CrO ₂ or Ru, Sn, Te, S for the purpose of improving the coercive force of CrO _2.
It is possible to use a material to which at least one of b, Fe, Ti, V, Mn and the like is added.

As the ferromagnetic alloy powder, Fe, Co, Ni, Fe-C
o, Fe-Ni, Fe-Co-Ni, Co-Ni, Fe
-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn
-Al, Fe-Co-V, etc. can be used, and Al, Si, Ti, Cr, M are used for the purpose of improving various characteristics.
You may add metal components, such as n, Cu, and Zn.

The binder that can be used in the magnetic layer may be any binder that has been conventionally used as a binder for magnetic recording media, such as vinyl chloride-vinyl acetate copolymer and vinyl chloride. -Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic acid Ester-
Vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer Polymer,
Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde Examples thereof include resins and mixtures thereof.

Further, in the magnetic layer, in addition to the binder and the ferromagnetic powder, a dispersant as an additive, an abrasive, an antistatic agent, a rust preventive agent,
Other lubricants and the like may be added.

The above-mentioned constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic paint, and the magnetic paint is applied onto a non-magnetic support. The solvent for the magnetic paint is acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or the like. Ketone type, ester type such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol monoethyl ether acetate, glycol ether type such as glycol dimethyl ether, glycol monoethyl ether and dioxane,
Aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene. Can be mentioned. The material of the non-magnetic support to which the magnetic coating material prepared with this organic solvent is applied may be any material that is usually used in this type of magnetic recording medium, for example, polyester such as polyethylene terephthalate. , Polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide, polyamide and polyamideimide. Examples include, paper, metals such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon. The form of this non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like.

Further, a magnetic recording medium to which the higher fatty acid ester of polyglycerin can be applied as a lubricant is a so-called coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic powder with a binder as described above. The present invention is not limited to this, and can be applied to a metal thin film type magnetic recording medium. This metal thin film type magnetic recording medium is formed by depositing a ferromagnetic metal on a non-magnetic support as a continuous film by plating or a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method or a sputtering method. As the magnetic layer. In this case, the ferromagnetic metal is F
In addition to metals such as e, Co and Ni, Co-Ni alloys, Co-
Pt alloy, Co-Ni-Pt alloy, Fe-Co alloy, F
e-Ni alloy, Fe-Co-Ni alloy, Fe-Co-B
An alloy, a Co-Ni-Fe-B alloy, a Co-Cr alloy, or an alloy to which a metal such as Cr or Al is added is used. This metal thin film type magnetic recording medium has a high magnetic flux density because it is not necessary to use a binder, and since the magnetic layer is formed as a very thin layer, it is useful for short wavelength recording and high density recording. .

[Action]

As described above, in the present invention, since the higher fatty acid ester of polyglycerin is used as the lubricant of the magnetic recording medium, the coefficient of friction is significantly reduced, and the fluctuation of the frictional force due to aging and the like can be suppressed.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1. Co-deposited γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride-vinyl acetate copolymer 15 parts by weight (UCC, VAGH) Polyurethane resin 7 parts by weight (Nippon Polyurethane Co., N-5033) Carbon (antistatic agent) 5 parts by weight Cr ₂ O ₃ 3 parts by weight Lecithin (dispersant) 1 part by weight Butyl stearate 1 part by weight Methyl ethyl ketone 150 parts by weight Methyl isobutyl ketone 150 parts by weight The above composition is mixed in a ball mill for 24 hours. Then, the mixture was taken out through a filter, and immediately before coating, 4 parts by weight of a curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added and stirred for 30 minutes. This magnetic paint was dried on a polyethylene terephthalate base having a thickness of 12 μm and the thickness after drying was 5 μm.
It was applied so as to obtain a magnetic field, subjected to magnetic field orientation treatment, dried, calendered and wound.

1.0% by weight hexane of oleic acid ester of polyglycerin (equivalent to n = 4, m = 4, which was estimated from the residual hydroxyl value. The same applies hereinafter) on the magnetic layer of the above-prepared tape. Using the solution, oleic acid ester was applied (top coat) so that the applied amount was 80 mg / m ^2, and cut into 1/2 inch width to obtain a sample tape.

Example 2. A 1.0 wt% hexane solution of isostearic acid ester of polyglycerin (n = 6, m = 5) was used on the magnetic layer of the magnetic tape prepared by the same method as in Example 1 above to prepare the isostearic acid ester. Coating amount is 80mg / m ²
(Top coat) to obtain a sample tape.

Example 3. On the magnetic layer of the magnetic tape prepared by the same method as in Example 1, the oleic acid ester of polyglycerin (n
= 6, m = 6) 1.0 wt% hexane solution was applied (topcoat) so that the application amount of isostearic acid ester would be 80 mg / m ² to obtain a sample tape.

Example 4. On the magnetic layer of the magnetic tape prepared by the same method as in Example 1, the oleic acid ester of polyglycerin (n
= 10, m = 5) in a 1.0 wt% hexane solution,
The oleic acid ester was applied (topcoat) so that the applied amount was 80 mg / m ² , to obtain a sample tape.

Example 5. On the magnetic layer of the magnetic tape prepared by the same method as in Example 1, the oleic acid ester of polyglycerin (n
= 10, m = 7) 1.0 wt% hexane solution,
The oleic acid ester was applied (topcoat) so that the applied amount was 80 mg / m ² , to obtain a sample tape.

Example 5. On the magnetic layer of the magnetic tape prepared by the same method as in Example 1, the oleic acid ester of polyglycerin (n
= 10, m = 7) 1.0 wt% hexane solution,
The oleic acid ester was applied (topcoat) so that the applied amount was 80 mg / m ² , to obtain a sample tape.

Example 6. A lauric acid ester of polyglycerin (n) was formed on the magnetic layer of the magnetic tape prepared in the same manner as in Example 1 above.
= 10, m = 10) 1.0 wt% hexane solution was applied (topcoat) so that the coating amount of lauric acid ester would be 80 mg / m ² to obtain a sample tape.

Example 7. Co-deposited γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride-vinyl acetate copolymer 15 parts by weight (UCC, VAGH) Polyurethane resin 7 parts by weight (Nippon Polyurethane Co., N-5033) Polyglycerin oleate 1 part by weight (n = 4, m = 2) Carbon (antistatic agent) 5 parts by weight Cr ₂ O ₃ 3 parts by weight Lecithin (dispersant) 1 part by weight Butyl stearate 1 part by weight Methyl ethyl ketone 150 Parts by weight Methyl isobutyl ketone 150 parts by weight The above composition was mixed in a ball mill for 24 hours, taken out through a filter, and immediately before coating, 4 parts by weight of a curing agent (Nippon Polyurethane Co., Coronate L) was added and stirred for 30 minutes. did. This magnetic paint was dried on a polyethylene terephthalate base having a thickness of 12 μm and the thickness after drying was 5 μm.
It was applied so as to obtain a magnetic field, subjected to magnetic field orientation treatment, dried and wound. This was calendered and then cut into a 1/2 inch width to prepare a sample tape.

Example 8. The oleic acid ester of polyglycerin of Example 7 (n =
4, m = 2) was replaced with isostearic acid ester of polyglycerin ((n = 6, m = 4), and the same magnetic coating material as in Example 7 was used except for the same method as in Example 7. A sample tape was created.

Example 9. The oleic acid ester of polyglycerin of Example 7 (n =
4, m = 2), oleic acid ester of polyglycerin (n = 10, m = 3) was used, the same magnetic paint as in Example 7 was used except for the above, and a sample was prepared in the same manner as in Example 7. I made a tape.

Example 10. The oleic acid ester of polyglycerin of Example 7 (n =
4, m = 2), oleic acid ester of polyglycerin (n = 10, m = 7) was used, the same magnetic paint as in Example 7 was used except for the above, and a sample was prepared in the same manner as in Example 7. I made a tape.

Comparative Example A magnetic coating material having the same composition as that of Example 1 was used, a magnetic layer was formed by the same method as in Example 1, and a top coat layer was not formed.

The friction coefficient and stick-slip of the sample tapes prepared in the above-mentioned respective examples and comparative examples were examined. The results are shown in the table below.

The coefficient of friction here is the low tape speed (0.4 mm
/ Sec) and the coefficient of friction between the magnetic layer surface and 1S stainless steel under a load of 50 g. In the table, in stick-slip, ⊚ is very good, ∘ is good, Δ is a little bad, and x is a bad one.

From this table, it can be seen that the magnetic recording medium according to the present invention has an extremely small coefficient of friction, satisfactory running performance, and stick-slip can be avoided.

〔The invention's effect〕

As is clear from the above description, in the present invention, since the higher fatty acid ester of polyglycerin is used as the lubricant of the magnetic recording medium, the friction coefficient is very small, the running property is good, and the running property is It is possible to obtain a magnetic recording medium that is excellent in durability without deterioration or change over time.

[Brief description of drawings]

FIG. 1 to FIG. 5 are enlarged cross-sectional views of a main part showing a configuration example of a magnetic recording medium to which the present invention is applied. 1 ... Non-magnetic support 2 ... Magnetic layer

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer formed on the non-magnetic support. (However, n represents an integer greater than or equal to 3.) The magnetic recording medium characterized by holding the higher fatty acid ester of polyglycerin shown by these.