JP2632036B2 - Magnetic recording media - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an improvement in a magnetic recording medium comprising a non-magnetic support, a magnetic layer and a backing layer.

(Description of Background of the Invention and Description of the Prior Art) Generally, a magnetic layer in which a ferromagnetic powder is dispersed in a binder is used as a magnetic recording medium for audio, video, and computer (disk, memory tape). A magnetic recording medium provided on a magnetic support is used.

In recent years, these magnetic recording media have been required to have high-density recording, and the signal / noise has been increased and the noise has been reduced by making the ferromagnetic powder finer, alloying the powder, filling the magnetic recording medium ultra-smoothly, etc. Has been achieved. Further, in order to perform high-density recording in the same time, it is necessary to reduce the writing speed and the fetching speed to the magnetic recording medium, and high-speed transport of the magnetic recording medium is required. Because of this high-speed transport suitability, running characteristics and charging characteristics,
A head cleaning property is indispensable. For this purpose, carbon black or a filer called an abrasive having a Mohs hardness of 8 or more is used. However, another major problem with these magnetic recording media is whether they can stably store magnetic recordings for decades. The problem of suitability for stable storage in a magnetic recording medium is mainly summarized in the following three points. That is, first, it is necessary to suppress a change in the magnetic properties of the ferromagnetic powder.
Deterioration of magnetic properties due to rust in alloy powder, Co-containing γ-Fe
The purpose is to suppress the deterioration of magnetic properties and the like due to a change in the abundance distribution of Co and Fe ⁺⁺ in particles in ₂ O ₃ . Secondly, deterioration of the binder is suppressed. It is known that a binder (binder) coating film is generally deteriorated by ultraviolet rays, temperature and humidity. (EFCuddhy, IEEE Trans.Ma
g., Mag 16, 4,558 (July 1980). It is known that vinyl chloride vinyl acetate resin and cellulose resin are less likely to deteriorate than polyurethane resin, and are used at about 10 to 60% by weight in the binder. Third, there is an increase in dropouts in magnetic recording media. The increase in the drop-out includes an intrinsic cause caused by the magnetic recording medium itself and an extrinsic one caused by dust in the outside world. Intrinsic drop-out is the generation of foreign matter from the magnetic recording medium and these are drop-outs.
Out of the head, or cause clogging of the head gap, causing a sparsing loss, thereby making it difficult to reproduce the magnetic recording. Many causes are known and examined for the generation of this foreign matter. For example, certain fatty acids,
Certain fatty acid esters, oligomers of polymeric supports,
Inorganic salts and the like. It is considered that the extrinsic dropout causes dust existing in the magnetic recording medium to attract and adhere to the surface layer of the magnetic recording medium due to an electrostatic cause to cause a spacing loss. Regarding the generation of static electricity, there is known a method of lowering the surface electric resistance of a magnetic recording medium, and it is known that carbon black or an antistatic agent is contained in or outside each constituent layer in the magnetic recording medium. I have. However, it has been extremely difficult with these techniques to suppress the occurrence of dropout due to exogenous dust. This is considered to be due to the fact that even if the electrostatic attraction of the extrinsic dust is suppressed, the magnetic recording medium is present in the dust environment in the atmosphere and must be stochastically exposed to the dust.
When exposed to dust, the dust is inevitably trapped between the tapes when the magnetic recording medium is wound up, which causes dropout.

Conventionally, various studies have been made with the aim of reducing the drop-out. For example, as disclosed in JP-A-61-85620, a polyurethane resin, a vinylidene chloride-acrylonitrile copolymer (for example, Saran resin), It has been proposed that a non-magnetic powder containing an isocyanate compound and a predetermined ratio of carbon black of fine particles having an average particle size of 30 to 150 mμ and carbon black of coarse particles having an average particle size of 160 to 600 μm. With such a technique, the coefficient of friction did not increase and no slippage occurred, so that the drop-out caused by these could be reduced and the S / N characteristics could be improved. However, it turned out that there was still room for improvement under severe conditions such as the 200-pass drop-out.

Therefore, as a result of further study, the present inventors clarified the causal relationship between the previously unknown mechanism of drop-out occurrence and the dust in the atmosphere to obtain a remarkable effect of improving storage suitability. Thus, the present invention has been accomplished.

(Object of the Invention) The present invention is to provide a magnetic recording medium which is excellent in storage suitability and free from drop-out, by clearly defining the surface free energy of each layer constituting the magnetic recording medium. Aim.

(Means for Solving the Problems) According to the present invention, a magnetic layer containing a ferromagnetic powder, a binder, carbon black, an abrasive and a lubricant is provided on a non-magnetic support, and a back layer containing a binder and a carbon black is formed on a magnetic layer. In a magnetic recording medium provided on the nonmagnetic support opposite to the layer, the surface free energy of the back layer is larger than the surface free energy of the magnetic layer by 1 dyn / cm or more, and the gloss of the magnetic layer is higher. Is 150 or more, and the back layer has a gloss of 2 to 7.

In the present invention, the magnetic layer preferably has a surface free energy of 40 to 55 dyn / cm and a surface electric resistance of 5 × 10 ¹⁰ Ω / cm ^2.
The back layer has a surface free energy of 45 to
The magnetic recording medium had a surface electric resistance of 60 dyn / cm and a surface electric resistance of 1 × 10 ⁵ Ω / cm ² or less.

(Operation and Effect of the Invention) In the magnetic recording medium of the present invention, the surface free energy of the magnetic layer is 40 to 55 dyn / cm, the surface free energy of the back layer is 45 to 60 dyn / cm, and the surface of the magnetic layer is If the surface free energy of the backing layer is larger than the free energy by 1 dB or more, the wound state becomes 2
Dust that is present between the layers and causes drop-out is absorbed by the back layer having a large surface free energy and does not remain on the magnetic layer side, thus reducing drop-out and It is considered that a magnetic recording medium having excellent video sensitivity and RF output can be obtained, and it is particularly effective for increasing drop-out related to storage. Further, by setting the surface electric resistance of the magnetic layer to 5 × 10 ¹⁰ Ω / cm ² or less and the surface electric resistance of the back layer to 1 × 10 ⁵ Ω / cm ² or less, dust existing in the air can be transferred to the magnetic recording medium. When combined with the above-described surface free energy effect, it is possible to obtain a magnetic recording medium that is particularly effective in reducing the increase in drop-out and has excellent video sensitivity and RF output. Further, the gloss of the magnetic layer is 150 or more, and the gloss of the back layer is 2
By setting to 7, the surface free energy of the magnetic layer and the backing layer can be stabilized, the drop-out increase can be reduced, and a magnetic recording medium excellent in video sensitivity and RF output can be obtained. In the above magnetic recording medium, the surface free energy of the back layer is more than 1 dyn / cm or more than the surface free energy of the magnetic layer, the gloss of the magnetic layer is 150 or more, and the gloss of the back layer is 2 to 7. Is an essential requirement of the present invention,
Out and RF output are improved.

(Detailed Description of the Invention) The surface free energy of the present invention is calculated by the formulas of Forks, Owens, and the formula of fields (FMFowkes: J. Phys. Chem. 66, 38).
2 (1962); 67,2583 (1963), DKOwens, RCWendt: JA
ppl. Polymer Sci., 13,1741 (1969); 14,1725 (1970),
Hata Toshio: Polymer, 17,594 (1698); Journal of the Adhesion Society of Japan, 8,13
1 (1972)), it can be determined from the contact angles of methylene iodide, ethylene glycol and water. These procedures can be referred to “Introduction to Polymer Properties” edited by The Society of Polymer Science, Japan (Kyoritsu Shuppan Co., Ltd., 1985), pp. 83-85. The measurement conditions for the contact angle are 23 ° C. and 70% RH.

The surface free energy of the present invention can be controlled by the composition and surface properties of the magnetic layer and the backing layer, and the production method.

The composition of the magnetic layer having a surface free energy of 40 to 55 dyn / cm according to the present invention comprises a ferromagnetic powder, a binder, a carbon black, an abrasive, and a lubricant.
Obtained at 100 / 18-40. Powders include ferromagnetic powders, carbon black, abrasives and the like. In particular, the binder comprises vinyl chloride resin and / or vinyl chloride vinyl acetate resin, polyurethane resin and polyisocyanate.
The weight ratio is preferably 45 to 55:15 to 25:20 to 35 by weight. The amount of the lubricant used in the magnetic layer of the present invention is a total of 100 ferromagnetic powders.
It is preferably 1 to 6 parts by weight based on parts by weight. The back layer having a surface free energy of 45 to 60 dyn / cm according to the present invention comprises a binder, carbon black, and other fillers, and a powder / binder ratio of 100/45 to 100 is obtained by weight. Powders include carbon black and other fillers. Particularly, the binder is composed of a phenoxy resin and / or a phenol resin, a polyurethane resin and / or an epoxy resin, and a polyisocyanate, and the 100-minute ratio is 20 to 50:40 to 70:10 to 40 by weight. The Young's modulus of the polyurethane resin or the like used in the present invention is 1 to 100 kg / mm ² .
Polyisocyanate is added to these materials in which carbon black is dispersed, and the Young's modulus of the back layer coating film is increased by 200.
To ~500kg / mm ^2.

In the magnetic recording medium of the present invention, the surface free energy of the magnetic layer is 40 to 55 dyn / cm, the surface free energy of the back layer is 45 to 60 dyn / cm, and the surface free energy of the magnetic layer is determined based on the surface free energy of the magnetic layer. A specific compositional method for increasing the surface free energy by at least / dyn / cm can be achieved by making a difference in the critical surface tension of the binder used for each layer. The value of the critical surface tension is described in, for example, “Chemistry and Industry”, Vol. 32, p. 898 (1979), Masanobu Motoyoshi, “Plastic Lubricity and Lubricant”, published by Nikkan Kogyo Shimbun (published in 1977), p. You can refer to “Chemical Handbook Basics II”, published by Maruzen in 1975. Teflon (18dyn / cm) <silicon resin (24dyn / cm) <polyethylene resin (31dyn / cm) <vinyl chloride resin (39dyn / cm) <nylon 66 (46dyn / cm) The value increases in the order of. In each resin, a -COO- group <-O
The value increases when a COO-group <-ONHCO- group is introduced. Generally, the value increases when a COOH group, SO ₃ H group, phosphate group, or the like is introduced. Accordingly, in the magnetic recording medium of the present invention, in order to set the surface free energy of the magnetic layer to 40 to 55 dyn / cm and the surface free energy of the back layer to 45 to 60 dyn / cm, the type of the binder used for the magnetic layer is required. Can be achieved by designing such that the critical surface tension is lower than the kind used for the backing layer. More specifically, when a vinyl chloride resin and a polyurethane resin are used for the magnetic layer, a resin having a lower critical surface tension than the vinyl chloride resin and a resin having a higher critical surface tension than the vinyl chloride resin, such as urethane, is used for the back layer. This can be achieved by using a resin, a nylon resin, or by forming a pseudo structure thereof in the backing layer.

The surface electric resistance of the magnetic layer of the magnetic recording medium of the present invention is 5 ×
In order to make it 10 ¹⁰ Ω / cm ² or less, an appropriate amount of conductive carbon black is added in an amount of 0.5 to 8 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. Include 8 copies. Further, the surface electric resistance of the back layer is set to 1 × 10 ⁵ Ω / cm ²
In order to achieve the following, the remaining filler is set to 30 parts by weight or less for 100 parts by weight of the carbon black.

The gloss of the magnetic layer of the magnetic recording medium of the present invention is set to 150 or more, and the gloss of the back layer is set to 2 to 7 by applying a super calender treatment after coating and limiting these conditions. Super calendar processing, temperature 70-120
C. and a linear pressure of 100 to 500 kg / cm are preferred. The supercalendering temperature is preferably higher than the melting point of the lubricant used for the magnetic layer in order to make the distribution of the lubricant uniform on the surface of the magnetic layer. The surface property of the magnetic layer was measured according to JIS-B0601-1982, and when the cut-off was 0.25 mm and the center line average surface roughness was 0.5 to 1.5 × 10 ^-2 μm for the magnetic layer, In this case, the thickness is preferably 3 to 12 × 10 ^-2 μm. In order to set the gloss of the magnetic layer of these magnetic recording media to 150 or more and the gloss of the back layer to 2 to 7 and to satisfy the above surface properties, the shear rate given to the coating solution immediately before coating is 4000 / sec or more. The viscosity at this time is 0.1 to 1 poise (25 ° C.). This viscosity is given by (shear stress) / (shear rate). For a discussion of these relationships, see Paint Flow and Pigment Puzzle Gillon by Patzton (TE
MPLE C. PATTON, “PAINT FLOW AND PIGMENT DISPER
SION "John Wiley and Sons, 1964).

The gloss value of the magnetic recording medium of the present invention is a value of specular gloss at a reflection angle of 45 degrees with respect to an incident angle of 45 degrees according to JIS Z8741, and is a relative value based on the specular gloss of black glass having a refractive index of 1.567 as 100%. It is a value expressed. This gloss value is considered to indicate a fine surface roughness of the surface layer of the magnetic recording medium. Generally, as the surface roughness of the surface layer of the magnetic recording medium increases, the surface free energy increases and the wettability easily occurs. Also, the smoother the surface roughness, the smaller the surface free energy,
Wetting is less likely to occur.

As the ferromagnetic powder used in the present invention, γ-Fe ₂ O ₃ , C
o-containing (deposition, denaturation, doping) γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co
Containing (deposition, modified, _{doped) Fe 3 O 4, FeOx,} Co -containing (deposition, modified, doped) FeOx of (X = 1.33~1.50), Cr
O ₂ and Rn, Te, Sb, Sr, Fe, Ti, V, Mn, CrO 2 containing at least one kind of _{Cr 2 O 3, Fe, Co} , Ni, Fe-CO alloy, Fe-
Ni alloy, Fe-Co-Ni alloy, Co-Ni-P alloy, Co-Ni-Fe
Known ferromagnetic powders such as -B alloy, Fe-Ni-Zn alloy, Ni-Co alloy, Co-Ni-Fe alloy, Fe-N alloy, Fe-Co-Cr alloy, and Mn-Bi alloy can be used.

As an example of the method for producing the ferromagnetic alloy powder, the following method can be mentioned.

(A) Method of reducing complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen: (b) Reduction of iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles Method: (c) Method for thermally decomposing a metal carbonyl compound: (d) Sodium borohydride,
Method of reducing by adding a reducing agent such as hypophosphite or hydrazine: (e) Method of depositing a ferromagnetic metal powder by electric field using a mercury cathode and then decomposing it with mercury: (f) Decomposition of metal at low pressure Method of obtaining fine powder by evaporation in active gas: The particle size of these ferromagnetic powders is about 0.005 to 1 micron and the ratio of shaft length / shaft width is about 1/1 to 50/1 . The specific surface area of these ferromagnetic powders is 1 m ² / g to 70 m
It is about ² / g. The water content of these ferromagnetic powders is 0.2 to
2.0 wt%. The water content of the coating solution when these ferromagnetic powders are used is 0.00 to 2.00 wt%. The surfaces of these ferromagnetic powders may be impregnated with a dispersant, a lubricant, an antistatic agent and the like described below in a solvent prior to dispersion and adsorbed for each purpose. These ferromagnetic powders
Sr, Pb, Mn, Ni, Cd, Cr, Al, Si, Ti, C within 1 wt%
It is preferable to include a heavy metal such as u or Zn. Alumina or the like may be applied to these ferromagnetic powders and melted.

As the ferromagnetic powder used in the present invention, plate-like hexagonal barium ferrite can also be used. Barium ferrite has a grain size of about 0.001 to 1 micron and a thickness of 1/2 to 1/20 of the diameter. The specific gravity of barium ferrite is 4-6 g / cc, a specific surface area is 1m ² / g~70m ² / g. The surface of these ferromagnetic powders has a dispersant, a lubricant,
An antistatic agent or the like may be impregnated and adsorbed in a solvent prior to dispersion for each purpose.

As the binder used for the magnetic layer and the back layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a softening temperature of 150 ° C. or less, an average molecular weight of 10,000 to 3000,000, and a degree of polymerization of about 50 to 2,000.For example, vinyl chloride vinyl acetate copolymer, vinyl chloride copolymer, vinyl chloride Vinylidene chloride copolymer, vinyl acrylonitrile chloride copolymer, acrylate acrylonitrile copolymer, acrylate vinylidene chloride copolymer, acrylate styrene copolymer, methacrylate acrylonitrile copolymer, methacrylate chloride Vinylidene copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyfuka vinyl, vinylidene acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyamide resin Vinyl butyral,
Cellulose derivatives (cellulose acetate butyrate,
Cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethylcellulose, methylcellulose, propylcellulose, methylethylcellulose, carboxymethylcellulose, acetylcellulose, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer , Amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof.

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, and becomes infinite with a molecular weight of 200,000 by coating, drying, and heating by reactions such as condensation and addition. Among these resins, those which do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin Mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol /
High molecular weight diol / triphenylmethane triisocyanate mixture, polyamine resin, polyimine resin, and mixtures thereof.

These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic powder to the binder in the magnetic layer is in the range of 5 to 300 parts by weight of the binder per 100 parts by weight of the ferromagnetic powder. The mixing ratio of the fine powder and the binder in the back layer is in the range of 30 to 300 parts by weight of the binder with respect to 100 parts by weight of the fine powder in a weight ratio. Additives include dispersants, lubricants, abrasives, antistatic agents, antioxidants, solvents and the like.

These thermoplastic resins, thermosetting resins, and reactive resins have a carboxylic acid, a sulfinic acid, a sulfonic acid, a sulfonic acid, a phosphoric acid, a sulfuric acid, a phosphon, a phosphine, a boric acid, a sulfate group as a functional group other than the main functional group. Acid groups such as acid ester groups, phosphoric ester groups, and alkyl ester groups thereof (these acidic groups may be in the form of Na salt, etc.), amino acids; aminosulfonic acids, sulfuric acid or phosphoric esters of amino alcohol, alkyl betaine type, etc. An amphoteric group of
Amino group, imino group, imide group, amide group, epoxy group, etc. It usually contains one or more hydroxyl groups, alkosyl groups, thiol groups, halogen groups, silyl groups, and siloxane groups, and each functional group is a resin. 1 x 10 ^-6 eq to 1 x per g
It is preferable to include 10 ^-2 eq.

Polyisocyanate is used as a curing agent of the binder used in the present invention, tolylene diisocyanate, 4,
4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate,
Isocyanates such as naphthylene-1,5-diisocyanate, o-toluidine isocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, isophorone diisocyanate, products of such isocyanates and polyalcohols, and products formed by condensation of isocyanates 2 to 15-mer polyisocyanate and the like can be used. The average molecular weight of these polyisocyanates is preferably from 100 to 20,000. Commercially available trade names of these polyisocyanates include Coronate L, Coronate HL, Coronate 20
30, Coronate 2031, Millionate MR, Millionate MT
L (manufactured by Nippon Polyurethane Co., Ltd., Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D
-202, Takenate 300S, Takenate 500 (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T-80, Sumidur 44S,
Sumidur PF, Sumidur L, Sumidur N, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, Desmodur T65, Desmodur 15, Desmodur R, Desmodur RF, Desmodur SL, Desmodur Z4273, etc. They can be used alone or in combination of two or more utilizing the difference in curing reactivity. Also, for the purpose of accelerating the curing reaction,
Hydroxyl group (butanediol, hexanediol, molecular weight
Compounds having an amino group (such as monomethylamine, dimethylamine, and trimethylamine) and catalysts of metal oxides can also be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates are preferably used in an amount of 5 to 40% by weight of the total amount of the binder.

Examples of the dispersant used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, linolenic acid, and stearolic acid. Ten~
26 fatty acids (R ₁ COOH, R ₁ is an alkyl group having 9 to 25 carbon atoms), alkali metals (Li, Na, K, NH ₄ ⁺
Etc.) or alkaline earth metals (Mg, Ca, Ba etc.), Cu, Pb
Metallic soaps, fatty acid amides of the above fatty acids; lecithin and the like are used. In addition, higher alcohols having 4 or more carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfates, phosphates, amine compounds and the like can also be used. In addition, polyalkylene oxides and their sulfates, phosphates, amine compounds, etc., sulfosuccinic acid, sulfosuccinates and the like can also be used. It is also possible to introduce Si and F substituents into these compounds in order to change the compatibility and properties with the binder. One or more of these dispersants are usually used, and one kind of the dispersant is added in an amount of 0.005 to 20 parts by weight based on 100 parts by weight of the binder 100. Regarding the method of using these dispersants, the dispersants may be applied to the surface of the ferromagnetic powder or non-magnetic powder in advance, or may be added during dispersion.

In addition, as a compound preferable as a dispersant, a surfactant such as a carboxylic acid or a phosphoric ester, or a fluorine-based surfactant Florad FC95, FC129, FC430, or FC431 can be used.

Lubricants and antioxidants used in the magnetic layer and the back layer of the present invention include molybdenum disulfide, boron nitride, graphite fluoride, calcium carbonate, barium sulfate, cesium oxide, titanium oxide, zinc oxide, tin oxide, and the like. Inorganic fine powder such as tungsten disulfide, acrylic styrene resin fine powder, benzoguanamine resin starch powder, melamine resin fine powder, polyolefin resin fine powder, polyester resin fine powder, polyamide resin fine powder, polyimide resin fine powder Powder, polyfluorinated ethylene resin fine powder, silicon oil, fatty acid modified silicone oil, graphite, fluorine alcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide wax, etc.), tetrafluoroethylene oxide wax, Polytetrafluoroglycol, perful B fatty acid, perfluoro fatty acid ester, perfluoroalkyl sulfate, perfluoroalkyl phosphate, alkyl phosphate, polyphenyl ether, monobasic fatty acid having 10 to 20 carbon atoms and monohydric alcohol having 3 to 12 carbon atoms Or a fatty acid ester composed of one or more of dihydric alcohol, trihydric alcohol, tetrahydric alcohol, and hexahydric alcohol, a monobasic fatty acid having 10 or more carbon atoms and a fatty acid ester of the fatty acid. Organic compound lubricants such as fatty acid esters composed of monohydric to hexahydric alcohols having 11 to 28 carbon atoms in total can be used. In addition, fatty acids having 8 to 22 carbon atoms, fatty acid amides, and fatty acid alcohols can also be used. Specific examples of these organic compound lubricants include butyl caprylate, octyl caprylate, ethyl laurate,
Butyl laurate, octyl laurate, ethyl myristate, butyl myristate, octyl myristate,
Ethyl palmitate, butyl palmitate, octyl palmitate, ethyl stearate, butyl stearate, octyl stearate, amyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, ann Hydrosorbitan tetrastearate, azohydrosorbitan ethylene oxide monostearate, oleyl oleate, oleyl alcohol, lauryl alcohol and the like can be used alone or in combination. As the lubricant used in the present invention, a so-called lubricating oil additive can be used alone or in combination, and an antioxidant (such as an alkylphenol), a rust inhibitor (such as naphthenic acid,
Alkenyl succinic acid, dilauryl phosphate, etc.),
Oily agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.), detergent / dispersant, viscosity index improver, pour point depressant, foam Agents. These lubricants are added in the range of 0.05 to 20 parts by weight based on 100 parts by weight of the binder.

As antioxidants, benzotriazine, benzothiazole, benzodiazone, heterocyclic compounds such as EDTA,
Hetero compounds can be used.

As the antistatic agent used in the present invention, graphite, carbon black, carbon black graft polymer,
Conductive powders such as tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-antimony oxide; natural surfactants such as saponin; alkylene oxide-based, glycerin-based;
Nonionic surfactants such as glycidol, polyhydric alcohols, polyhydric alcohol esters, and alkylphenol EO adducts; higher alkylamines, cyclic amines, hydantoin derivatives, amidoamines, esteramides, quaternary ammonium salts, pyridine and other complexes Cationic surfactants such as rings, phosphoniums or sulfoniums;
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group; amino acids; amphoteric surfactants such as aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and alkyl betaine type Agents and the like are used. These surfactants may be added alone or as a mixture. Also, these surfactants may be 1mg / m ² ~550mg / m ² overcoat on the surface of the magnetic recording medium. The amount of these surfactants used in the magnetic recording medium is 0.01 to 100 parts by weight of the ferromagnetic powder.
~ 10 parts by weight. These are used as antistatic agents, but are sometimes applied for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and application aids.

As the carbon black used in the present invention, furnace black for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific examples of abbreviations of these carbon blacks in the United States include SAF, ISAF, I
ISAF, T, HAF, SPF, FF, FEF, HMF, GPF, APF, SRF, M
PF, ECF, SCF, CF, FT, MT, HCC, HCF, MCF, LFF, RCF
And those classified into D-1765-82a of the US ASTM standard can be used. The average particle size of these carbon blacks used in the present invention is 5 to 1,
000 millimicron (electron microscope), nitrogen adsorption method specific surface area is 1-1500 m ² / g, PH is 2-13 (JIS standard K-6221-1982
Method), dibutyl phthalate (DBP) oil absorption is 5-2,000
It is ml / 100 g (JIS standard K-6221-1982 method). The water content of these carbon blacks used in the present invention is from 0.00 to
20 wt%. The size of the carbon black used in the present invention is 5 to reduce the surface electric resistance of the coating film.
A 100 mm carbon black is used, and a 50-1,000 mm carbon black is used to control the strength of the coating film. Fine carbon black (less than 100 millimicron) for smoothing to reduce spacing loss in order to control the surface roughness of the coating film
Coarse carbon black (50 millimicrons or more) is used for the purpose of roughening and reducing the coefficient of friction. As described above, the type and amount of the carbon black are properly used depending on the purpose required for the magnetic recording medium.

Further, these carbon blacks may be surface-treated with a dispersant described later or grafted with a resin. In addition, the furnace temperature for producing carbon black was set at 2,000
Those obtained by treating at a temperature of 0 ° C. or more and partly graphitizing the surface can also be used. Also, a hollow carbon black can be used as a special carbon black.

These carbon blacks are ferromagnetic powders for the magnetic layer
It is desirable to use 0.1 to 20 parts by weight based on 100 parts by weight. Carbon black and the dynamic value of carbon black that can be used in the present invention are, for example, "Carbon Black Handbook",
You can refer to the Carbon Black Association, edited by (Showa 46).

As the abrasive for the magnetic layer and the back layer used in the present invention, a material having a polishing action or polishing action generally used, such as α-alumina, γ-alumina, α-γ-alumina,
Fused alumina, silicon carbide, chromium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main component: corundum and magnetite), garnet, silica, silicon nitride, boron nitride, molybdenum carbide, carbonized Tungsten, titanium carbide, quartz,
Materials such as tripoly, diatomaceous earth, dolomite and the like having a Mohs hardness of 6 or more, more preferably a Mohs hardness of 8 or more are used in combination of 1 to 4 types. These abrasives have an average particle size of 0.005 to 5 Micron sizes are used, particularly preferably 0.01 to 2 microns.
These abrasives are used in an amount of 0.01 to 2 with respect to 100 parts by weight of the binder.
It is added in the range of 0 parts by weight.

Dispersion of the present invention, kneading, as the organic solvent used in the application, acetone, methyl ethyl ketone in any ratio,
Ketones such as methyl isobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran; alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol and methyl cyclohexanol; methyl acetate, ethyl acetate;
Ester systems such as butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol monoethyl ether; ether systems such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene, toluene, xylene, cresol, and chlor Tar-based (aromatic hydrocarbons) such as benzene and styrene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde, hexane and the like can be used.

The method of kneading is not particularly limited, and the order of addition of each component can be appropriately set. For the preparation of the magnetic paint and the back layer paint, a conventional kneading machine such as a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, a Tsegvari (Szegvar)
i), attritor, high-speed impeller, disperser, high-speed stone mill, high-speed impact mill, disper, kneader,
A high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a disperser, a homogenizer, a single screw extruder, a twin screw extruder, and an ultrasonic disperser can be used. For more information on kneading and dispersing technology, see TC
"Paint Flow and" by PATTON
Pigment Dispersion "
Pigment Day Pasgillon) 1964 John Wiley & S
Ons, published by Jillon Willie and Sons, Shinichi Tanaka, Industrial Materials, Vol. 25, 37 (1977), and in the references cited in the book, and in combination with these kneading and dispersing machines for continuous processing. Liquid and apply. It is also described in specifications such as U.S. Patent Nos. 2,581,414 and 2,855,156. Also in the present invention, a magnetic paint and a backing layer paint can be prepared by kneading and dispersing according to the method described in the above-mentioned book or the cited reference of the book.

The formation of the magnetic layer is performed by dissolving in an organic solvent any combination of the above compositions and the like, and coating and drying the coating solution on a support. When used as a tape, the thickness of the support is 2.5 to 1
It is preferably about 00 microns, preferably about 3 to 70 microns. Thickness of 0.03 to 10 even in disk or card form
mm, and in the case of a drum, it can be used in a cylindrical shape. Examples of the material include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyamide, and polysulfone. In addition to plastics such as, for example, metals such as aluminum and copper, and ceramics such as glass can also be used. Prior to coating, these supports may be subjected to corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, dust removal treatment, metal deposition treatment, and alkali treatment.

As a method of applying the magnetic layer and the back layer on the support, air doctor coating, blade coating,
Air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, bar coat, etc. can be used, and other methods are also possible. Is described in detail in “Coating Engineering” published by Asakura Shoten, pp.253-277 (published in 1963).

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting in a desired direction while immediately drying the ferromagnetic powder in the layer, if necessary, and then the formed magnetic layer is dried. The transport speed of the support at this time is usually 10
m / min ~ 1,000m / min, drying temperature 20 ℃ ~ 130 ℃
Is controlled by If necessary, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape. These manufacturing methods include filler surface treatment,
It is preferable that the steps of kneading / dispersing, coating, heat treatment, calendering, EB treatment, surface polishing treatment, and cutting are continuously performed. Further, the steps can be divided into several steps as required.

In these steps, the temperature and humidity are controlled, and the temperature is 10 ° C. to 130 ° C., and the humidity is expressed as 5% in the air.
~ 20 g / kg (dry air).

(Examples) Hereinafter, the present invention will be described more specifically with reference to examples.
It will be readily understood by those who are involved in the art that the components, proportions, order of operation and the like shown herein can be changed without departing from the spirit of the present invention.

Therefore, the present invention should not be limited to the following examples. In the examples, parts in the examples are parts by weight.

[Example 1] [I] of the following magnetic layer composition was placed in a kneader and kneaded well, and then [II] was additionally charged and kneaded well.
I] was added and mixed and dispersed to prepare a magnetic paint.

Magnetic layer composition [I] Co-containing γ-Fe ₂ O ₃ powder 300 parts (nitrogen adsorption specific surface area: 45 m ² / g powder Hc: 900 Oe) Vinyl chloride resin 38 parts (SO ₃ H, epoxy group-containing, MR110, Japan) 18 parts of polyurethane resin (Chrispon 7209, manufactured by Dainippon Ink) 12 parts of carbon black (Vulcan XC72, manufactured by Cabot Corporation, average particle size 30m)
μ) Abrasive: 18 parts of α-Al ₂ O ₃ (Sumitomo Chemical Co., Ltd., HIT100) Abrasive: 3 parts of Cr ₂ O ₃ (manufactured by Nippon Chemical Industry, Sl average particle size 0.1 μm) Oleic acid 3 parts Cyclohexane 150 parts [II] butyl acetate 850 parts tert-butyl myristate 3 parts [III] polyisocyanate 21 parts (Coronate 3040, manufactured by Bayer AG) Stearic acid 3 parts butyl acetate 100 parts After adjusting the viscosity of this magnetic paint, a 19 μm non-magnetic support was used. Was applied to a polyethylene terephthalate having a dry film thickness of 5.0 μm, and the resultant was magnetically oriented with a 3,000 gauss magnet, dried, and subsequently calendered to form a magnetic layer. On the back side of the non-magnetic support with the magnetic layer,
The following backing composition [I] was kneaded and dispersed in a ball mill, [II] was added thereto, mixed and stirred to prepare a backing solution, and applied to a dry film thickness of 2.0 μm to form a backing layer.

Back layer composition [I] Carbon black 85 parts (MTCI: Nitrogen adsorption non-surface area: 10 m ² g Average particle size 250 mμ, manufactured by Sevalco) Carbon black 15 parts (Conductex SC Nitrogen adsorption specific surface area: 200 m ² / g average particle Polyurethane polycarbonate resin 35 parts (FJ2, manufactured by Dainichi Seika) 10 parts of phenoxy resin (PKHH, manufactured by Union Carbide) Copper oleate 0.1 part Methyl ethyl ketone 700 parts Cyclohexane 300 parts [II] Polyisocyanate 10 Parts (Coronate 3040, manufactured by Nippon Polyurethanes) Lubricant 0.1 part (silicone, KF69, manufactured by Shin-Etsu Chemical Co., Ltd.) Lubricant 1 part (oleic acid) 100 parts of methyl ethyl ketone Manufactured.

Example 2 A tape was prepared in the same manner as in Example 1 except that the binder of the backing layer was changed as shown in Table 1, and a sample was prepared in the same manner as in Example 1 except for the above.

Example 3 In Example 1, the binder for the back layer was 5 parts of vinyl chloride vinyl acetate resin (SO ₃ H, containing an epoxy group, MR110, manufactured by Zeon Corporation) and polyurethane resin (Crespon 72).
09, manufactured by Dainippon Ink and 14 parts of polyisocyanate (Coronate 3040, manufactured by Nippon Polyurethane Co., Ltd.).

[Comparative Example 1] The following composition was placed in a ball mill, kneaded and dispersed for 48 hours, and then 10 parts of a polyisocyanate compound ("Coronate L-75" manufactured by Nippon Polyurethane KK) was added and kneaded and dispersed for another 1 hour. Then, the mixture was passed through a filter having an average pore diameter of 1 μ to obtain a coating solution for a magnetic layer.

Co-containing γ-Fe ₂ O ₃ powder 100 parts Vinyl chloride-vinyl acetate-maleic anhydride 15 parts Acid copolymer ("MPR-TM" manufactured by Nissin Chemical) Nitrocellulose 5 parts Polyurethane resin 6 parts ("Chrisbon 6119" manufactured by Dainippon Ink) Carbon black 3 parts (average particles) Size 20mμ) Chromium oxide 3 parts Oleic acid 2 parts Butyl stearate 1 part Stearic acid 0.5 parts Fatty acid-modified silicone 2 parts Oleic acid amide 0.5 parts Butyl acetate 240 parts Methyl ethyl ether 120 parts The above magnetic layer coating solution is 20μ polyethylene. After coating on a terephthalate substrate surface with a lippers roll so as to have a dry thickness of 6 μm, and drying and kneading and dispersing a coating solution for a back layer having the following composition in a ball mill for 70 hours, a polyisocyanate compound (“Coronate L75” Japan Polyurethane KK
And kneading and dispersing for an additional hour, and after kneading and dispersing,
The mixture was passed through a filter having an average pore diameter of 3 μ to obtain a coating solution for the back layer. The coating solution for the back layer was coated on a polyethylene terephthalate substrate opposite to the magnetic layer by a reverse roll so as to have a dry thickness of 2 μm and dried.

This tape was subjected to a super calender roll treatment and then slit to a width of 1 inch to prepare a sample.

The surface free energy of the magnetic layer and the backing layer was measured using a Perkin-Elmer goniometer at 23 ° C. and 70%, based on the description of “Introduction to Polymer Properties” (Kyoritsu Shuppan Co., Ltd., 1985), pp. 84-85. Was measured for vinegar, methylene iodide, and ethylene glycol, and determined by the Fowkes equation.

Comparative Example 2 In Example 3, a tape was prepared by changing the binder of the back layer as shown in Table 1, and a sample was prepared in the same manner as in Example 1 except for the above.

[Comparative Example 3] In Example 1, the super calendar condition was 90 ° C,
A tape was prepared by changing the linear pressure from 300 kg / cm to 65 ° C. and a linear pressure of 300 kg / cm, and other samples were prepared in the same manner as in Example 1.

〔Evaluation method〕

Drop-out (DO) At room temperature (23 ° C, 40% RH), the Sony BVH500
After measuring the drop-out with a VTR (initial value), repeated 200 passes, video tape at 40 ° C, 80% RH
After storing at room temperature for 1 week (relative humidity), return to room temperature, measure drop-out again (time value), and calculate the difference between the drop-out aging value per minute and the initial drop-out value. Was.

RF output The RF output before and after the above test was obtained as a relative value.

As is clear from the examples shown in Table 1, the magnetic recording medium of the present invention has excellent drop-out and RF output characteristics. In Comparative Examples 1 to 3, it is recognized that the surface free energies of the magnetic layer and the backing layer of the magnetic recording medium are not properly balanced. In the case of Comparative Example 3, even if the surface free energy of each magnetic layer is properly balanced, the surface gloss value is inappropriate, and the effectiveness of the present invention is supported.

Claims (2)

(57) [Claims] A magnetic layer containing a ferromagnetic powder, a binder, a carbon black, an abrasive and a lubricant is provided on a non-magnetic support, and a back layer containing a binder and a carbon black is provided on the non-magnetic support opposite to the magnetic layer. In a magnetic recording medium provided on a magnetic support, the surface free energy of the back layer is larger than the surface free energy of the magnetic layer by 1 dyn / cm or more, and the gloss of the magnetic layer is 150 or more. A magnetic recording medium, characterized in that the layer has a gloss of 2 to 7, 2. The magnetic layer having a surface free energy of 40 to 55.
dyn / cm, its surface electric resistance is 5 × 10 ¹⁰ Ω / cm ² or less, and the surface free energy of the backing layer is 45-60 dyn / cm.
^2. The magnetic recording medium according to claim 1, wherein the surface electric resistance is 1 × 10 ⁵ Ω / cm ² or less.