JPH0785455A - Magnetic recording tape - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a magnetic recording tape having good dispersibility of magnetic powder and excellent electromagnetic conversion characteristics and running durability. [Structure] In a magnetic recording tape having a plurality of layers formed by dispersing magnetic powder or non-magnetic powder in a binder on a non-magnetic support, and having a magnetic layer on the uppermost layer, the end of the uppermost magnetic powder is The heat of adsorption of the compound having a functional group —COOH is 30 joules / mole or more and 80 joules / mole or less, and the heat of adsorption of the compound having a functional group —SO ₃ Na at the end is 10 joules / millimol or more 40 joules / A magnetic recording tape which is less than or equal to mmol and contains 0.01 to 1.00 mmol / g of a negative functional group in the binder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to improvement of dispersibility of ferromagnetic powder in the medium and practical adjustment of electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art In recent years, magnetic recording media useful as recording and reproducing elements in information processing equipment have high electromagnetic conversion characteristics and high precision, and high recording capacity.
It is required to be a composition substance that guarantees good runnability and durability, and in particular, it is required to keep these characteristics in good balance.

Regarding the electromagnetic conversion characteristics, it is necessary to make the ferromagnetic powder finer and reduce the particulate noise as the image quality of magnetic recording media tends to increase.

However, the finer the magnetic powder, the greater the magnetic interaction and the poorer the dispersibility. As a result, the output characteristics are poor, the binding property with the binder is deteriorated, and the durability of the magnetic recording medium is deteriorated.

In particular, when a magnetic powder having a large surface area or a magnetic powder having a large number of active points is used, water tends to be adsorbed on the surface thereof, and the binding property between the magnetic powder and the binder is likely to be impaired.

On the other hand, if a low molecular weight component such as fatty acid is added and used as a dispersant in order to improve the dispersibility of the magnetic powder, the durability of the magnetic recording medium deteriorates especially under high temperature and high humidity.

To solve these problems, Japanese Patent Laid-Open No. 1-19
Japanese Patent Nos. 9316 and 2206020 disclose a method for measuring the amount of stearic acid adsorbed on magnetic powder, and a technique relating to the affinity of magnetic powder with a covalent binder containing a negative functional group.

Quantification of the polar point on the surface of the magnetic powder by the amount of adsorption is an effective means, but it does not quantitatively represent the adsorption strength. In consideration of dispersion, the idea of strength is an important index as well as quantity, and the heat of adsorption was adopted as a parameter that expresses this. This method is capable of directly and accurately measuring the amount of heat when adsorbed. The chemical adsorption described here is a relatively strong adsorption in which the adsorbate and the adsorption medium are adsorbed in the form of ions, and other hydrogen adsorption, aggregation due to van der Waals force, and the like are considered weak adsorption.

However, in these techniques, magnetic powder is put into a solution of stearic acid to be adsorbed, and the supernatant liquid is quantified. Therefore, since it is an indirect method of determining the adsorbed amount, chemical adsorption (strong adsorption) is actually performed. Is dissolved in the solution and
Alternatively, there is a difficulty in that it is difficult to distinguish from the amount of weak adsorption. (Because the magnetic powder first chemically adsorbs with stearic acid, excess stearic acid that exceeds the adsorption point does not strongly adsorb with the magnetic powder anymore, but exists in a free state.) It is possible to obtain it by analyzing the magnetic powder adsorbed with FT-IR, but in this case the accuracy was low and many measurement points were required, so the efficiency was poor.

Further, Japanese Unexamined Patent Publication (Kokai) No. 5-062160 discloses that the surface of the magnetic powder is defined by the adsorption amount of stearic acid, stearylamine, vinyl chloride and polyurethane resin. However, this does not similarly require the strength of adsorption. In reality, the required characteristics cannot be obtained if there is a large amount of weak adsorption.

In order to satisfy the dispersion stability, the functional group contained in the binder is particularly preferably a metal salt of sulfonic acid, and the basic point related to this adsorption is limited to the determination of the adsorption amount, and the adsorption strength is taken into consideration. It had the drawback of not doing it.

The magnetic powder may contain various kinds of elements, but when the element contained in the surface shell layer is boron or silicon, the surface is oxidized by the gradual oxidation step and the water mixed in the step is added. As a result, it changes to oxides, hydroxides, etc., making it easier to form oxidation points on the surface of the magnetic powder. On the contrary, alkali and alkaline earth metals such as sodium and calcium facilitate the formation of basic points. In particular, sodium easily forms a strong basic point, and those that become divalent cations such as calcium and barium have a large adsorption amount, and as a result, compared to those that contain a large amount of sodium,
The heat of adsorption per molecule is low.

Some elements, like cobalt, migrate to the inside, and as a result, there is little effect on the surface.

If the water content is large, weak adsorption increases, and the heat of adsorption per molecule becomes low. Furthermore, since the basic point is closed, the adsorption point is reduced, and the heat of adsorption is similarly reduced.

The acidic point and the basic point thus formed have appropriate values, so that they strongly chemically bond with the functional groups in the binder to obtain good dispersion stability, but on the contrary, if they are too large. Adsorbs the lubricant and hinders running performance and durability.

[0016]

In view of the above circumstances, an object of the present invention is to provide a magnetic recording tape having good dispersibility of magnetic powder and excellent balance of electromagnetic conversion characteristics and running durability. is there.

[0017]

The above object of the present invention can be achieved by the following constitutions.

In a magnetic recording tape having a plurality of layers formed by dispersing magnetic powder or non-magnetic powder in a binder on a non-magnetic support and having a magnetic layer on the uppermost layer, the uppermost magnetic powder contains the magnetic powder. The heat of adsorption with a compound having a functional group -COOH at the end is 30 joules / mole or more and 80 joules /
The amount of heat of adsorption with a compound having a functional group —SO ₃ Na at the end is 10 Joules / mmol or more and 40 Joules / mmol or less, and 0.01 to
A magnetic recording tape containing 1.00 mmol / g of a negative functional group.

The present invention will be described in detail below.

Therefore, the heat of adsorption per molecule of the compound having the functional group --COOH and the compound having --SO ₃ Na at the end of the present invention was determined by using a flow microcalorimeter, and the adsorption strength was shown by this. The magnetic powder of the uppermost layer related to the present invention has a functional group at the end of the present invention
The heat of adsorption per molecule of the compound having COOH is 30 joules / mmol or more and 80 joules / mmol or less, preferably 40 joules / mmol or more and 70 joules / mmol or less, and the compound having the functional group -SO ₃ Na at the end of the present invention Of 1
The heat of adsorption per molecule must be 10 Joules / mmol or more and 40 Joules / mmol or less, preferably 15 Joules / mmol or more and 35 Joules / mmol or less.

The heat of adsorption of the compound having —COOH of the present invention is
30 since the heat absorption of the compound having a -SO ₃ Na in Joules / mmole below and the present invention is less point of attachment to the binder is less than 10 Joules / mmole, it is not preferable because the bonded state hard, the former is 80 joules / Mmol,
If the latter exceeds 40 joules / mmol, the active sites will be excessive, and the magnetic powder will often bond with additives other than the binder, and the coating film will deteriorate, which is also undesirable.

Examples of the compound having a functional group --COOH at the end of the present invention include stearic acid, myristic acid and the like, and fatty acids described in JP-A No. 2-110818, p.130-131.

Examples of the compound having a functional group --SO ₃ Na at the terminal of the present invention include sodium dioctylsulfosuccinate and sodium alkylsulfonate (having carbon numbers C ₆ -C).
₂₀ ), and compounds such as sodium benzenesulfonate.

The specific surface area of the ferromagnetic powder by the BET method is usually 30 m ² / g or more, preferably 40-80 m ² / g.
Is preferred.

The shape of the ferromagnetic powder is not particularly limited, and for example, any shape such as needle-like, spherical or ellipsoidal shape can be used.

The magnetic layer of the magnetic recording medium of the present invention comprises preferably a plurality of magnetic layers having ferromagnetic powder dispersed in a binder and provided on a non-magnetic support.

At least one of the layers contains a ferromagnetic metal powder, and examples thereof include Fe-Al metal powder, Fe, Ni metal powder, and the like, which can also be used in other layers.

The ferromagnetic powder is, for example, Co-containing γ-Fe.
₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, Co-containing FeOx (4/3 <X <3 /
2) Powder, Fe-Al metal powder, Fe-Ni metal powder, CrO
₂ powders, modified hexagonal ferrite powders such as Co-Ti modified barium ferrite and Co-Ti modified strontium ferrite, and ferromagnetic powders described in JP-A-3-113820, p.4.

In the present invention, a nonmagnetic auxiliary constituent layer may be provided in addition to the magnetic layer, and α-Fe ₂ is contained in the nonmagnetic layer.
A non-magnetic powder such as O ₃ , TiO ₂ , Cr ₂ O ₃ and α-Al ₂ O ₃ is used.

The ferromagnetic metal powder particles containing aluminum, sodium, calcium or aluminum in the particle surface shell layer according to the present invention are preferably acicular iron alloy magnetic particle powders. After coating with aluminum or boron compound and sodium compound and calcium compound and aluminum compound, 300 to 6
The acicular hematite particles coated with aluminum oxide or sodium compound, calcium compound and boron oxide are subjected to heat treatment in the temperature range of 00 ° C, and the acicular hematite particles are then heated at 300 to 500 ° C. It can be obtained by heating and reducing in the temperature range.

The acicular crystal goethite particle powder in the present invention is a suspension containing ferrous hydroxide particles obtained by mixing a well-known aqueous solution of ferrous salt with an equivalent amount or more of an alkaline solution.
Oxygen-containing gas in a suspension containing FeCO ₃ obtained by reacting an aqueous solution of a ferrous salt with an alkali carbonate by ventilating an oxygen-containing gas at a temperature of pH 11 or higher and a temperature of 80 ° C. or lower. Can be obtained by any method, such as a method of aerating air to carry out an oxidation reaction, and use particles having a major axis of 0.1 to 0.4 μm and an axial ratio (major axis: minor axis) of 5: 1 to 20: 1. You can In the above-mentioned goethite formation reaction, Co, Ni, Zn, Al, Mn, Cu or other metal ions that are usually added to improve the properties of the target acicular iron alloy magnetic particle powder may be present. Good.

As the boron compound in the present invention, KB
O ₂ , H ₃ BO ₃ , HBO ₂ , B ₂ O _{3 and the} like can be used. The acicular crystal goethite particles can be coated with the boron compound by mixing and stirring an aqueous solution containing boron and the acicular crystal goethite particles, and then filtering and drying.

As the aluminum compound in the present invention, aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum hydroxide, sodium aluminate, alumina sol and the like can be used. The coating of needle-shaped goethite particles with an aluminum compound is performed by mixing and stirring an aqueous solution containing aluminum and needle-shaped goethite particles, or if necessary, mixing and stirring and neutralizing with an alkaline aqueous solution or an acidic aqueous solution, and then filtering. Alternatively, it can be performed by drying. As the potassium and calcium compounds, an alkaline aqueous solution such as sodium hydroxide or calcium hydroxide is used. P of acicular goethite particles
When H is adjusted, it may be used as an alkaline solution for coating, or may be mixed with a small amount at the time of washing with water for coating.

The heating and firing temperature in the present invention is 300 to 600.
℃. If the temperature is lower than 300 ° C, it is difficult to densify the particles, and therefore the shape of the particles cannot be retained during heating in the subsequent reduction step, and the coercive force of the acicular iron alloy magnetic particle powder is However, the SFD cannot be reduced to 0.5 or less. As for the reason why SFD is not improved, when the heating and firing temperature is lower than 300 ° C,
Inadequate recrystallization causes uneven shape anisotropy due to the particle shape distribution after reduction and uneven crystal anisotropy due to the structural distribution of Fe, B and Co. it is conceivable that. If it exceeds 600 ° C, sintering occurs between particles and the particles lose their shape.

The heat reduction temperature in the present invention is 300 to 500.
℃. When the temperature is lower than 300 ° C., the reduction reaction is insufficient and it is impossible to obtain acicular iron alloy magnetic particle powder having a large saturation magnetization. If the temperature exceeds 500 ° C., sintering occurs between particles and the particles are deformed, and the coercive force of the acicular iron alloy magnetic particle powder decreases.

The acicular iron alloy magnetic particle powder obtained in the present invention has a major axis of 0.1 to 0.4 μm and an axial ratio (major axis: minor axis).
It is in the range of 5: 1 to 15: 1.

The acicular iron alloy magnetic particle powder after heat reduction in the present invention is prepared by a known method, for example, by immersing in an organic solvent such as toluene and after replacing the atmosphere after reduction with an inert gas, It can be taken out into the air by a method such as gradually oxidizing with oxygen while gradually increasing the oxygen content in the inert gas.

The binder used in the present invention is preferably a binder having a negative functional group.

The negative functional groups include --SO ₃ M ¹ and --OSO.
₂ M ¹ , -OSO ₃ M ¹ , -COOM ₂ , -OH and monovalent-{(OM ² ) (OM
³ )} P = O, -O {(OM ² ) (OM ³ )} P = O (where,
M ¹ is a hydrogen atom or an alkali metal, M ² and M
Each of ³ is a hydrogen atom, an alkali metal or an alkyl group. Further, M ² and M ³ may be different from each other or may be the same. ) Can be mentioned.

In the present invention, it is important to use a binder composed of a polymer containing a negative functional group in an amount commensurate with the active point of the ferromagnetic powder, that is, the acidic point and the basic point.

That is, the negative functional group of the binder having a negative functional group in the present invention is 0.01 to 1.00 mmol / g.
It is preferably 0.05 to 0.50 mmol / g.

When the amount of the negative functional group is within the above range, the dispersibility of the ferromagnetic powder is improved, and as a result, the output of the magnetic recording medium is increased and the running durability is also improved.

On the other hand, if it deviates from the above range, these effects may not be sufficiently exhibited.

The molecular weight of the polymer having the negative functional group is usually 2,000 to 70,000, preferably 4,000 to 50,000. If this molecular weight exceeds 70,000, the viscosity of the magnetic coating material may exceed the permissible range and the object of the present invention may not be achieved.

On the other hand, if the molecular weight is less than 2,000, an unreacted portion will be generated and a low molecular weight component will remain in the stage of curing by the added curing agent after coating the magnetic coating on the non-magnetic support. It may deteriorate the physical properties of the coating film.

When the polymer having a negative functional group is used, the compounding amount thereof is usually 2 to 15 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

If this blending ratio is less than 2 parts by weight, the desired effect to be obtained when the polymer having a negative functional group is blended may not be sufficiently exhibited. If it is more than 15 parts by weight, electromagnetic conversion characteristics and still durability may be deteriorated.

In the present invention, the durability of the magnetic layer can be improved by using a polyisocyanate type curing agent together with the polymer having a negative functional group.

Examples of the polyisocyanate type curing agent include tolylene diisocyanate, diphenylmethane diisocyanate, etc., and JP-A-3-13820.
Nos. 9 to 10 can be used.

The amount of the above curing agent used is usually 5 to 80 parts by weight based on the total amount of the binder.

In the present invention, as a binder, together with the vinyl chloride copolymer having a negative functional group and a polyurethane resin, a thermoplastic resin, a thermosetting resin, a reactive resin, which has been conventionally used in magnetic recording media, An electron beam irradiation curable resin or a mixture thereof can be used together.

Examples of the thermoplastic resin include, for example, vinyl chloride-vinyl acetate copolymer and the like, and JP-A-3-11382.
No. 0 p.10 to 11 can be mentioned.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, and the like, and the resins described in JP-A-3-113820, p.11.

Examples of the electron beam irradiation curable resin include maleic anhydride type and urethane acryl type resins, and resins described in JP-A-3-113820, p.12.

The blending ratio of polyurethane and vinyl chloride copolymer is a weight ratio of polyurethane (PU) resin: vinyl chloride copolymer, and is usually 9: 1 to 1: 9, preferably 8: 2 to 2:
8 If the mixing ratio is out of the above range, the electrode conversion characteristics of the magnetic layer in the magnetic recording medium of the present invention may be deteriorated, or the dispersibility of the ferromagnetic powder may be deteriorated.

In the present invention, as the dispersant which is an optional component,
For example, lecithin, fatty acids, etc.
It is possible to add the dispersant described in No. 1 to the magnetic layer. These may be used alone or in combination of two or more.

In the present invention, since the binder and the ferromagnetic powder specified as described above are used, the amount of the dispersant added can be suppressed to a necessary minimum amount, and the amount of the dispersant added is usually 100 parts by weight of the ferromagnetic powder. , 10 parts by weight or less, preferably 3 parts by weight or less.

By thus reducing the amount of the dispersant such as fatty acid added, the running durability of the magnetic recording medium can be improved especially under high temperature and high humidity.

The magnetic layer in the magnetic recording medium of the present invention is
It may contain a lubricant.

When a fatty acid and / or a fatty acid ester is contained as a lubricant, while exhibiting the respective characteristics of both, the defects that occur when used alone are offset, the lubrication effect is improved, and the still image durability and running are improved. Stability, S / N ratio, etc. can be improved. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight per 100 parts by weight of the magnetic powder, 0.5 to 8.0 parts by weight.
Better parts by weight. When the amount of fatty acid is out of this range, the dispersibility of the magnetic powder is lowered and the running property of the medium is also lowered, and when the amount is large, the fatty acid is leached out and the output is easily lowered. In addition, the amount of fatty acid ester added is
0.1 to 10 parts by weight is preferable to 100 parts by weight, and 0.2 to 8.5 parts by weight is more preferable. If the amount of ester deviates from this range and the amount of ester decreases, the effect of improving the running property becomes poor, and if the amount of ester increases, the amount of ester oozes out and the output tends to decrease.

In order to achieve the above effects more favorably, the weight ratio of fatty acid to fatty acid ester is preferably fatty acid / fatty acid ester = 10/90 to 90/10. It should be noted that fatty acids also have a dispersive effect, and it is considered that the use of fatty acids can reduce the amount of another low molecular weight dispersant used, and the Young's modulus of the magnetic recording medium can be improved accordingly.

The fatty acid may be monobasic or dibasic. Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms are preferable. Examples of the fatty acid include myristic acid, stearic acid, and the like, and the fatty acids described in JP-A No. 2-110818, p.130 to 131.

Examples of the fatty acid ester include butyl stearate, butyl palmitate, etc., and JP-A-2-110818.
Examples thereof include fatty acid esters described in No. p.181. In addition to the above fatty acids and fatty acid esters, other lubricants (for example, silicone oil; carboxylic acid modified or ester modified may be used), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide. , Α-olefin oxide and the like may be added to the magnetic layer.

The mixing ratio of the lubricant is the ferromagnetic powder 10
Generally, 20 parts by weight or less, preferably 10 parts by weight, relative to 0 parts by weight.
It is less than or equal to parts by weight. If this blending ratio exceeds 20 parts by weight, the amount of the lubricant may become excessive and stains may easily adhere to the surface of the magnetic layer.

The magnetic layer may further contain an abrasive and an antistatic agent in addition to the above various components.

Examples of the abrasive include α-alumina, chromium oxide and the like, and those described in JP-A-2-110818, p.131.

When carbon black is used in combination in the magnetic layer, it is further advantageous in terms of improving running properties and electromagnetic conversion characteristics, the dispersibility is slightly improved, and the amount of residual solvent in the magnetic layer is smaller than that of the magnetic layer. Has a preventive effect.

If light-shielding carbon black is used as such carbon black, the degree of light shielding can be increased. Examples of carbon black for shading include Raven 2000 (specific surface area 190 m, manufactured by Columbia Carbon Co., Ltd.)
² / g, particle size 18Emumyu) carbon black in JP-A 2-110818 Patent p.129 forth and the like.

As the conductive carbon black,
For example, Conductivity (Con
ductex) 975 (BET value (hereinafter abbreviated as BET) 250 m ² / g,
DBP oil absorption (hereinafter abbreviated as DBP) 170ml / 100g, particle size 24
mμ) Conductex 900 (BET 125m ² / g, particle size 27m
and carbon black described in JP-A-2-110818, p.129.

Another carbon black that can be used in the present invention is Conductex-SC. (BET220m ² / g, DBP 115ml / 1, made by Columbia Carbon Co., Ltd.
00g, particle size 20mμ), Vulca made by CABONET
n) 9 (BET140m ² / g, DBP 114ml / 100g, particle size 19mμ)
Examples thereof include those described in JP-A-2-110818, p.129-130.

The antistatic agent or the dispersant described later does not have only a single action, but one compound may act as a lubricant and an antistatic agent, for example.

Therefore, the above-mentioned classification in the present invention shows the main actions, and the action of the classified compounds is not limited by the action shown in the classification.

Examples of the material for forming the non-magnetic support for laminating a plurality of magnetic layers described above include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose triacetate and cellulose diacetate. Cellulose derivatives such as; and polycarbonates,
Examples include plastics such as polyamide, polyamideimide, and polyimide. Further, metals such as Cu, Al and Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can be used.

The form of the non-magnetic support is not particularly limited, and may be tape-shaped, sheet-shaped, card-shaped, disk-shaped, drum-shaped or the like, depending on the form.
Various materials can be selected and used as needed.

The thickness of the support is usually 3 to 100 μm, preferably 5 to 50 μm in the case of tape or sheet.
Is. Further, in the case of a disk shape or a card shape, it is usually 30 to 100 μm. Further, in the case of a drum shape, a cylindrical shape can be used, for example, a shape corresponding to a recorder to be used.

A back coat layer may be provided on the surface (back surface) of the non-magnetic support, on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. .

An intermediate layer (for example, an adhesive layer) may be provided on the surface of the non-magnetic support on which the magnetic layer is provided for the purpose of improving the adhesiveness between the magnetic layer and the non-magnetic support. it can.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

The magnetic recording medium of the present invention comprises:
It can be produced by kneading and dispersing a magnetic layer forming component such as polyurethane having a negative functional group in a solvent to prepare a magnetic coating material, and then coating and drying the magnetic coating material on the non-magnetic support.

Examples of the solvent used for kneading / dispersing the components for forming the magnetic layer include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and ketone-based solvents such as cyclohexanone, and JP-A-3-13820.
The solvents described in Nos. P. 18 to 19 can be used.

In kneading the composition of the magnetic paint components, the ferromagnetic powder and other magnetic paint components (hereinafter, these may be referred to as raw materials) are simultaneously or individually added to the kneading machine. For example, first, the ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and further kneading is continued to obtain a magnetic coating material.

For kneading and dispersing, various kneaders can be used. Examples of this kneader include, for example, a two-roll mill and a three-roll mill.
The kneading machine described in p.20 of No. 3820 can be mentioned.

The coating solution of the magnetic layer-forming component thus prepared is coated on the non-magnetic support by a known method.

Examples of the coating method that can be used in the present invention include gravure roll coating and
In addition to wire bar coating, etc.
The method described in 20 can be mentioned.

The thickness of the magnetic layer thus coated is such that the dry thickness of the uppermost magnetic layer is 0.1 to 5 μm, and particularly 0.2.
˜4 μm, and the total dry thickness of each magnetic layer is usually 1
~ 6 μm.

Thus, after applying the magnetic layer-forming component,
In the undried state, magnetic field orientation treatment is performed if necessary, and further surface smoothing treatment is usually performed using a super calender roll or the like.

Then, a magnetic recording medium can be obtained by cutting into a desired shape.

The magnetic recording medium of the present invention can be used as a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or as a floppy disk by cutting into a disk shape. . Further, like a normal magnetic recording medium, it can be used in a card shape, a cylindrical shape, or the like.

[0089]

EXAMPLES The present invention will be described in detail with reference to examples.

Example 1 The magnetic powder, non-magnetic powder shown in Table 1 and the following raw materials were thoroughly stirred and mixed using a ball mill, and a polyfunctional isocyanate (Coronate L: manufactured by Nippon Polyurethane Co.) was added to this mixture. Add 5 parts each, average pore size 1μm
It was prepared by filtering with a filter.

Upper-layer coating formulation Fe-Al-based metal powder 100 parts Vinyl chloride copolymer (polymerization degree 300, containing -SO ₃ Na 0.07 mmol / g) 15 parts Polyester type polyurethane resin (toluene diisocyanate, 1,6 hexanediol, Adipic acid, -SO ₃ Na 0.07 mmol / g content average Mw = 20000) 10 parts Alumina powder 5 parts Carbon black 3 parts Myristic acid 2 parts Stearic acid 2 parts Palmitic acid butyl ester 2 parts Stearic acid butyl ester 1 part Cyclohexanone 100 parts Methyl ethyl ketone 150 parts Toluene 50 parts Lower layer coating formulation Co Coated Fe ₃ O ₄ powder 100 parts Vinyl chloride copolymer (polymerization degree 300, -SO ₃ Na containing 0.07 mmol / g) 15 parts Polyester type polyurethane resin (toluene diisocyanate, 1 , 6-hexanediol, adipic acid, -SO ₃ Na0.07mmol / g containing an average Mw = 20000) 10 parts polyester type polyurea Tan resin (4,4'-diphenylmethane diisocyanate, 1,4-butanediol, adipic acid, -SO ₃ Na0.05mmol / g containing, average Mw = 20000) 2 parts 10 parts myristic acid palmitic acid butyl ester 2 parts Cyclohexanone 100 parts Methyl ethyl ketone 150 parts Toluene 50 parts Next, using the lower layer coating material and the upper layer coating material, the layer in contact with the non-magnetic support is the lower layer, the layer in contact with the lower layer is the upper layer, and the thickness is 14
The thickness of the bottom layer after drying is 3 μm and the thickness of the top layer is 0.5 μm on a wide polyethylene terephthalate film of μm.
Has become.

The film having the two layers was then heated to 70 ° C.
It was processed by a super calender roll at 300 Kg / cm.

Further, a back coat layer coating material having the following composition was prepared.

Carbon black (Conductex 975 of Colombia Carbon Co., Ltd.) 11 parts Urethane elastomer (Goodrich Co. Estan 5701) 6 parts Nitrocellulose (Celnova BTH1 / 2 of Asahi Kasei Corporation) 4 parts Methyl ethyl ketone 80 parts Toluene 60 parts The above composition is ball milled. After sufficiently stirring and mixing with the above, 5 parts of polyfunctional isocyanate (Coronate L) was added, and the mixture was filtered with a filter having an average pore diameter of 1.5 μm. The obtained back coat layer coating material was applied to the back surface of the wide magnetic film so that the dry thickness was 1.1 μm. This film was cut into a width of 8 mm to prepare a magnetic tape for video.

In Examples 2 to 4 and Comparative Examples 1 to 5, upper layer magnetic powder, lower layer magnetic or non-magnetic powder, vinyl chloride copolymer and polyester type polyurethane resin were used.
Created in the same manner except that the SO ₃ Na content is changed as shown in Table 1.
It was measured under the same conditions.

Each of the above samples was evaluated and measured under the following conditions.

(Measurement Method of Heat of Adsorption) Flow microcalorimeter (MARK-3Vi manufactured by MICROSCAL) was used. For example, stearic acid as a compound having a functional group —COOH at the terminal and sodium dioctylsulfosuccinate as a compound having —SO ₃ Na were dissolved in cyclohexane, respectively, and the one adjusted to 0.8 wt% was adsorbed.

First, Bridge range 100 mV, amplifier 500
μV, set the flow rate of the micro pump to 3.3 ml / h, take about 0.1 g of the sample powder, and let cyclohexane flow from the micro pump No. 1. When the amount of heat becomes stable, this point is set to 0, the micro pump No. 2 is switched to, and the cyclohexane solution of stearic acid is allowed to flow. At this time, the amount of heat generated by adsorption is expressed as the heat of adsorption per 1 g of the powder (adsorption heat unit:
Millijoule / g).

At this time, at the same time, the differential refractometer 830-RI is provided downstream.
(Made by JASCO) is attached, the adsorption state is measured in advance using polytetrafluoroethylene (PTFE) as a sample powder, and the unadsorbed state in the sample measurement is determined from the curve of the unadsorbed substance obtained by this measurement. The curve was subtracted to obtain the adsorption amount per 1 g of the powder. (mg / g) amplifier 200
With the same setting except for μV, for example, the functional group --SO ₃
Sodium dioctyl sulfosuccinate was measured as a compound having Na, and the heat of adsorption and the amount of adsorption were determined.

Heat of adsorption per molecule of compound = [heat of adsorption (m
J / g) / adsorption amount (mg / g)] x (molecular weight) x 1000 ^-1 (J / mmo
Calculated from l) *.

* Unit: Joule / mmole FIG. 1 (a) is a diagram showing a change in heat quantity with time and adsorption.

FIG. 1 (b) is a diagram showing the change in the refractive index of the carrier solvent with respect to the time and the concentration of the solution that is eluted without being adsorbed.

FIG. 1 (a): Using the above flow microcalorimeter, first, using cyclohexane, calorific value 2
The point where the (vertical axis) does not change is taken as the heat quantity 0 (3). If you switch from cyclohexane to a solution of stearic acid (SA) or sodium dioctylsulfosuccinate (SDSS) (time 5 when you switch from cyclohexane to SA or SDSS) and start measuring the calorific value, heat will be generated due to the adsorption of the magnetic powder. Draw a peak like 1 (a).

The amount of heat becomes equal to 0 when no more adsorption occurs. The heat of adsorption 1 becomes equal to the area of the portion sandwiched by the curves in FIG. 1 (a). The horizontal axis represents time 4 (unit: minutes).

FIG. 1B: Next, the refractive index is measured using polytetrafluoroethylene (PTFE) as a sample powder using the flow microcalorimeter and the differential refractometer. Similarly, in FIG. 1 (a), cyclohexane is used and the refractive index 10 of the cyclohexane is determined to be 0. Here, switching from cyclohexane to a solution of stearic acid (SA) or sodium dioctylsulfosuccinate (at the time of switching from cyclohexane to SA or SDSS 11) When measuring the refractive index, most of the above solution was not adsorbed on the PTFE. Is eluted as unadsorbed and the change in refractive index 7 with the concentration is drawn as a curve.

Next, when the same operation is performed using the magnetic powder as the sample powder, a curve shown by the difference 6 in the refractive index with respect to cyclohexane due to the concentration change is drawn. The two curves are superposed in FIG. 1B, and the portion surrounded by the curves is the change in the refractive index corresponding to the concentration of the solution adsorbed by the magnetic powder. Based on this, the adsorption amount 12 is obtained by converting from the concentration of the solution. In FIG. 1 (b), 8 is the refractive index (vertical axis), and 9 is
Represents time (unit: minutes).

Still other evaluation items and measuring methods are shown below.

(B) RF-output, chroma-output; Sony EV-BS300 deck using the noise meter 925C manufactured by Shibasoku, and inputting the signals shown below, the output when reproduced is SONY Hi8 (P6-90). ) To the value (dB).

RF-output: 7MHz Chroma-output: 500KHz (b) Squareness ratio; Using a vibrating sample type magnetometer manufactured by Toei Industry Co., Ltd., when Hm is 5K Oe, (residual magnetic flux density) / (saturation magnetic flux) The density) was calculated.

(C) Dropout increase; 40 ° C, 80% RH
In the environment, when the dropout when the tape was run for 100 hours on the EV-BS300 deck made by Sony was more than the first dropout, it was ×, and when it did not increase, it was ○.
It was evaluated. (15μs size, -12dB depth or more, 1
(Value in minutes) (d) Shed; When the tape is run for 100 hours in an environment of 40 ° C and 80% RH, the rank of dirt on the head is A when not dirty and when it is slightly dirty. Is B, when it is dirty it is C, when it is very dirty it is D
It was evaluated.

(E) Edge damage: The tape after running for 100 hours was visually observed, and when the edge portion was broken, it was evaluated as x, and when not broken, it was evaluated as o.

The results are shown below.

[0113]

[Table 1]

[0114]

[Table 2]

As is clear from the results shown in Table 2, the examples of the present invention are superior to the comparative examples. However, the unit (J / mmol) in Table 1 is Joule / mmol.

[0116]

The magnetic recording tape according to the present invention has an effect that the dispersibility of the magnetic powder is good and excellent electromagnetic conversion characteristics and running durability are well balanced.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in the refractive index due to changes in the amount of heat due to adsorption and changes in the solution concentration according to the present invention.

[Explanation of symbols]

 1 Heat of adsorption 2 Heat quantity (millijoules) 3 Heat quantity 0 4 hours (horizontal axis, unit: minutes) 5 Switching point from cyclohexane to SA or SDSS 6 Difference in refractive index to cyclohexane with concentration change 7 Change in refractive index with elution concentration 8 Refractive index (vertical axis) 9 hours (horizontal axis) 10 Refractive index of cyclohexane 11 Switching point to SA or SDSS 12 Adsorption amount

Claims (1)

[Claims] 1. A plurality of layers comprising magnetic powder or non-magnetic powder dispersed in a binder on a non-magnetic support,
In a magnetic recording tape having a magnetic layer as the uppermost layer, the heat of adsorption of a compound having a functional group --COOH at the end of the magnetic powder in the uppermost layer is 30 joules / mmol or more and 80 joules / mol or more.
And in mmol or less, the heat of adsorption compounds with a terminal functional group -SO ₃ Na is not more than 10 joules / mmole than 40 joules / mmol, and the binder 0.01.
A magnetic recording tape comprising a negative functional group of 00 mmol / g.