JPH0618077B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk, and more particularly to surface slipperiness of the medium.

(Prior Art) Generally, a magnetic recording medium is manufactured by applying a magnetic coating material containing at least magnetic powder, a binder and the like on a support and then drying it. In these magnetic tapes for video, computers, audio, etc., high tape performance is required. Stillness durability and stable running property are particularly required for video tapes having a high relative speed of tapes. Therefore, not to mention the abrasion resistance of the tape itself,
It is extremely important to reduce the friction of the tape during running.

So far, various lubricants, such as silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide or lauric acid, myristic acid, etc., for the purpose of reducing the friction of the magnetic layer,
Monobasic fatty acids with 4 or more carbon atoms (Japanese Patent Publication No.
No.) is known to be added.

However, even if these lubricants are added, sufficient characteristics have not yet been obtained, and an undesirable phenomenon such as blooming cannot be prevented.

Furthermore, with the development of magnetic recording equipment and the expansion of the range of applications, magnetic recording media (hereinafter collectively referred to as magnetic tapes) have high recording density, high-performance electromagnetic conversion characteristics, and good tape physical properties such as surface slipperiness. Is being requested.

The above-mentioned electromagnetic conversion characteristics or physical properties of the tape are reduced by reducing the frictional resistance of the magnetic powder or the tape surface contained in the magnetic layer or other magnetic tape constituent layers by reducing the contact surface, or various filler particles or antistatic. Particle size and specific surface area (BET value: unit m ²
/ G), and it is required that the BET value is large especially in terms of electromagnetic conversion characteristics and recording density. However, a large BET value tends to impair the surface slip property of the tape physical properties.

(Object of the Invention) It is an object of the present invention to provide a magnetic tape having good surface slipperiness regardless of the composition of constituent layers including the magnetic layer of the magnetic tape.

(Structure and Operation and Effect of the Invention) The above-mentioned object of the present invention is a magnetic recording medium comprising a support and a constituent layer provided for magnetic recording, wherein the constituent layer contains a fatty acid, The amount of the non-polar hydrocarbon solvent extracted from the constituent layer is 5 to ³⁰ mg / cm ³ in total with respect to the volume of the constituent layer provided on the same side of the support, and the magnetic powder used for the constituent layer is A BET value of 30 to 50 m ² / g is achieved by a magnetic recording medium.

In the present invention, the constituent layer means a magnetic layer, an overcoat layer, a backcoat layer, an adhesive layer, etc., which are directly involved in magnetic recording or directly or indirectly involved in electromagnetic conversion characteristics and tape physical properties. It is a layer provided on the support in order to smoothly perform recording, recording retention or reproduction by electromagnetic conversion with good performance.

The nonpolar hydrocarbon solvent according to the present invention is, for example, cyclohexane or n-hexane.

In the extraction operation, a certain amount of the constituent layers was peeled off, and the mixture was immersed in boiling water, for example, cyclohexane for 4 hours for immersion. After the residue was removed, cyclohexane was distilled off and the residue was analyzed by gas chromatography to determine the extraction amount. .

Next, the present invention will be described in detail.

As described above, it is required that the BET value of various solid powders including the magnetic powder contained in the constituent layers of the magnetic tape be large, and carbon black or the like has a BET value of 200.
About m ² / g is general, and even magnetic powders of 30 m ² / g to 100 m ² / g are targeted.

Even in a fine powder having a BET value of this level, most of the fatty acids added are sorbed on the surface or the inner surface thereof, and the amount extracted with cyclohexane or the like may be only 5 wt% of the added amount.

The specific surface area indicated by the BET value varies depending on the material, but of course the same material can be used in its manufacturing process and the elapsed time after manufacture, or the size of the secondary particle structure such as continuous beads or tufts (structure level). Fluctuates depending on.

Also, the adsorption or sorption efficiency differs depending on the material or pH, and the adsorption area naturally changes depending on the amount of fine powder contained in the constituent layers.

The added fatty acid is immobilized by the above-mentioned factors and deviates from the lubricating action, and at the same time, the binder structure used and the hardening agent used, and the degree of hardening thereof cause a difference in the diffusivity of fatty acids and the like, and free lubrication that contributes to the lubricating action. The dose will be different.

As described above, the effective amount of the surface lubricity of the fatty acid-based lubricant added varies a lot depending on the composition of the constituent layers, and it is difficult to determine the effective amount as an ambiguous paste.

Therefore, it is not possible to establish a technical system relating to surface slipperiness at least by determining the amount of lubricant added based on one part of the constituent layer. That is, for example, the addition amount of the fatty acid-based lubricant determined based on the weight of the magnetic powder has no technical meaning as far as the surface slipperiness is concerned.

The so-called surface slipperiness is distinguished from the effect of the matting agent which improves the slippage by reducing the contact area of the surface.

Based on the above-mentioned circumstances, the present invention determines the effective amount of lubricant that is actually involved in the surface slipperiness and has a meaning as a technical system by the free amount of the lubricant in the constituent layers.

In addition, according to the results of the analysis, the effective lubricant amount deviates from the range specified by the present invention even in the case where the conventional magnetic powder having a BET value not sufficiently large and the sample using the filler are sampled. is doing.

The free fatty acid contained in the constituent layer in the present invention is 5 to 30 per unit volume of the constituent layer provided on the same side of the support.
Although it is mg / cm ^{3, if} it is less than this range, the surface slipperiness is insufficient, and if it exceeds this range, blooming and other disadvantages occur, which is not preferable.

Fatty acids as the lubricant used in the present invention include, for example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and the like having 8 to 18 carbon atoms. Fatty acids (R represented by R-COOH is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); the above-mentioned fatty acid alkali metal (Li, Na, K, etc.) or alkaline earth metal ( M
g, Ca, Ba, etc.) and the like.

Examples of magnetic materials include γ-Fe ₂ O ₃ and Co-containing γ-F.
e ₂ O ₃ , Co deposition γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co deposition F
oxide magnetic materials such as e ₃ O ₄ and CrO ₂ , or Fe, Ni, Co,
Fe-Ni alloy, Fe-Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, F
e-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, F
Various ferromagnetic materials such as e-Co-Ni-P alloys, Co-Ni alloys, Co-P alloys, Co-Cr alloys, and metal magnetic powders containing Fe, Ni, and Co as the main components can be used. As additives to these metal magnetic materials, Si, Cu, Zn,
Elements such as A, P, Mn, and Cr or compounds thereof may be contained. Further, hexagonal ferrite such as barium ferrite and iron nitride are also used.

Examples of the binder for forming the constituent layer according to the present invention include polyurethane having abrasion resistance. It has a strong adhesive force to other substances, is mechanically tough against repeated stress or bending, and has good wear resistance and weather resistance.

When a fibrin resin and a vinyl chloride copolymer are contained in addition to polyurethane, the dispersibility of the magnetic powder and the like in the magnetic layer is improved and the mechanical strength thereof is increased. However, the layer becomes too hard only with the fiber-based resin and the vinyl chloride-based copolymer, which can be prevented by the above-described inclusion of polyurethane.

As usable fibrin-based resins, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. The vinyl chloride copolymer may be partially hydrolyzed. The vinyl chloride-based copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate alcohol,
Examples thereof include vinyl chloride-vinyl acetate-maleic anhydride and vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride.

Further, regarding the entire binder composition, the ratio of the above-mentioned polyurethane and the other resin (the total amount of the fiber-based resin and the vinyl chloride-based copolymer) is 90/10 to 20 / by weight.
It has been confirmed that 80 is preferable, and 85/15 to 30/70 is more preferable. If the amount of polyurethane is out of this range, poor dispersion tends to occur and the still properties are likely to deteriorate, and if the amount of other resins is large, the surface properties are likely to be poor and the still properties also deteriorate. The physical properties of the coating film become less favorable overall.

As the binder according to the present invention, a mixture of the above-mentioned binder and a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation curable resin may be used. As the thermoplastic resin, the softening temperature is 150 ° C or lower, the average molecular weight is 10,
000 to 200,000, having a degree of polymerization of about 200 to 2,000, for example, acrylic ester-acrylonitrile copolymer,
Acrylic acid ester-vinylidene chloride copolymer, acrylic acid ester-styrene copolymer and the like are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and is condensed after coating and drying,
Those which are insolubilized by a reaction such as addition are used. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin and the like.

As the electron beam irradiation curable resin, an unsaturated prepolymer,
For example, maleic anhydride type, urethane acryl type, polyester acryl type, polyether acryl type, polyurethane acryl type, polyamide acryl type, etc., or as a polyfunctional monomer, ether acryl type, urethane acryl type, phosphate ester acryl type, aryl type , Hydrocarbon type, and the like.

In order to improve the durability of the constituent layers of the magnetic tape according to the present invention, the constituent layers can contain various curing agents,
For example, an isocyanate can be contained.

Aromatic isocyanates which can be used are, for example, tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI) and addition of these isocyanates with active hydrogen compounds. There is a body, etc., and the average molecular weight is 100 to 3,0
A range of 00 is preferred.

On the other hand, as aliphatic isocyanate, hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TM
DI) and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates with active hydrogen compounds, those having a molecular weight of 100 to 3,000 are preferable. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds and active hydrogen compounds are preferable.

If necessary, the coating material forming the constituent layers of the magnetic tape of the present invention may contain additives such as a dispersant, a matting agent, a lubricant other than the above-mentioned lubricant, an abrasive and an antistatic agent.

As the dispersant, for example, lecithin, higher alcohol having 12 or more carbon atoms, and sulfuric acid ester can be used. Moreover, a commercially available general surfactant can also be used. These dispersants may be used alone or in combination of two or more. When using these dispersants in the magnetic layer is added in the range of 1 to 20 parts by weight to 100 parts by weight of the magnetic material, when used in the backcoat layer 2 to 20 parts by weight to 100 parts by weight of the binder Part may be added.

As the matting agent, organic powders or inorganic powders are used individually or as a mixture.

The organic powder used in the present invention is preferably acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin. Powders, polyfluorinated ethylene resin powders, etc. can also be used, and as inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α −Fe ₂ O
₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide.

As the lubricant other than the above-mentioned lubricant, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, etc. are used.

Further, an abrasive can also be used for the magnetic layer, and as the abrasive, generally used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main component is Corundum and magnetite), titanium dioxide, etc. are used. As these abrasives, those having an average particle diameter of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm.
belongs to. These abrasives are added in the range of 1 to 20 parts by weight with respect to 100 parts by weight of magnetic powder.

In addition to carbon black, as an antistatic agent, graphite, tin oxide-antimony oxide-based compounds, titanium oxide-tin oxide-antimony oxide-based compounds, conductive powders such as carbon black graft polymers; natural surfactants such as saponin Alkylene oxide-based, glycerin-based, glycidol-based nonionic surfactants; pyridine and other heterocycles, phosphonium or sulfonium-based cationic surfactants; carboxylic acids, sulfonic acids,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups and phosphoric acid ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols and the like.

You may add these surfactant individually or in mixture. These are used as antistatic agents, but may be used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and coating aid.

As the solvent to be blended in the above paint or a diluent solvent at the time of applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate, ethyl acetate , Esters such as butyl acetate, ethyl lactate, ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, ethylene chloride, Halogenated hydrocarbons such as carbon tetrachloride, chloroform and dichlorobenzene can be used.

Further, as the support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Cu, A and Zn,
Ceramics such as glass, BN, Si carbide, porcelain and pottery can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of film or sheet, 30 μm to 10 mm in the case of disc or card, and cylindrical in the case of drum. It is used and its type is determined according to the recorder used.

As a coating method for forming the constituent layer by coating the constituent layer coating material on a support, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure A coat, a kiss coat, a cast coat, a spray coat or the like can be used, and other methods are also possible.

The constituent layers are applied by such a method. The magnetic layer is subjected to a treatment for orienting the magnetic powder in the layer if necessary, and then the constituent layers of the formed magnetic tape are dried. If necessary, the surface is smoothed or cut into a desired shape to manufacture the magnetic tape according to the present invention.

(Example) Next, the present invention will be described with reference to an example.

Example 1 Magnetic paint formulation Magnetic powder 100 parts Carbon black 5 〃 Polyester urethane 15 〃 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 15 〃 Cyclohexanone 130 〃 Toluene 130 〃 Fatty acid (palmitic acid) The characteristics of the magnetic powder and carbon black in which the adhesion is a problem are as follows.

Magnetic powder A BET value 50m ² / g, γ-Fe ₂ O _{3 at} pH 10, magnetic powder B BET value 30m ² / g, γ-Fe ₂ O _{3 at} pH 7, carbon C BET value 100m ² / g, pH 7, black 〃 D 〃 200 〃 〃
8. The above formulations were kneaded and dispersed in a ball mill, coated and dried, and subjected to supercalender treatment to obtain inventive samples 1 to 4 and comparative samples (1) and (2).

The magnetic layers of these samples were removed, and the samples were refluxed and extracted in cyclohexane for 4 hours.

Table 1 shows the amount of fatty acid added and the amount of fatty acid extracted per cm ^{3 of the} magnetic layer.

Next, the measurement results of dynamic friction coefficient and blooming of these samples are shown in Table-2.

Measurement of characteristics: Measurement of dynamic friction coefficient: After leaving the magnetic tape in an atmosphere of 25 ° C and 55% relative humidity (atmosphere in rainy weather) for 24 hours (humidity adjustment), measure the friction coefficient of each magnetic tape. The dynamic friction coefficient was measured using a rotating drum type surface measuring instrument manufactured by Shinto Kagaku Co., Ltd., with a rod having a diameter of 4 mm, a load of 30 g, and a rotation speed of 159 rpm.

The surface of the blooming tape was visually evaluated with a 100 × microscope.

Table 1 shows that the amount of free lubricant extracted is different even if the binder is the same and the lubricant is the same, and it can be seen that the dynamic friction coefficient and the degree of blooming differ depending on the amount. .

Example 2. Addition amount of fatty acid, γ-Fe ₂ O ₃ (Magnetic powder C: BET value 25 m ²
/ G and γ-Fe ₂ O ₃ (magnetic powder D: BET value 55 m ² / g) were changed as shown in Table 3 to prepare a sample in the same manner as in Example 1 of the present invention. The characteristics were measured.

The above results are shown in Table-3.

From Table-3, the present invention (the amount of fatty acid extracted is 5 to 30 mg / c)
It can be seen that in the range of m ³ ), the tape has excellent slipperiness and blooming.

(Effects of the Invention) According to the present invention, the effective lubricant amount for surface slipperiness is determined irrespective of the composition of magnetic tape constituent layers and the number of constituent layers, and there is no variation among product lots, and in terms of production technology and quality assurance. It has brought great convenience.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a support and a constituent layer provided for magnetic recording, wherein the constituent layer contains a fatty acid, and the fatty acid is a nonpolar hydrocarbon solvent from the constituent layer. by extraction amount, the volume per 5 to 30 mg / cm ³ of the component layers provided on the same side of the support, BET value of the magnetic powder to be used for constituting layer is 30m ² / g~50m ² / g A magnetic recording medium characterized by: