JPH10320758A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve surface property, to attain stable and fact application of a magnetic coating material having high characteristics and to decrease the production cost by incorporating an aluminum coupling agent into a lower magnetic layer of a laminar magnetic layer having a two-layer structure. SOLUTION: Coating characteristics to obtain good surface roughness are more required for the lower magnetic layer than the durability of the coating film. By adding an aluminum coupling agent into the lower magnetic layer, coupling groups (hydrophilic groups) in the molecule are adsorbed to the surface of the magnetic powder, while hydrophobic groups has good affinity with the binder to fill the space among magnetic powder particles with the binder. Thus, the coupling agent acts as a dispersant to improve the dispersibility of the magnetic powder. The amt. of the aluminum coupling agent is preferably 0.5 to 5 pts.wt. to 100 pts.wt. of the magnetic powder. The aluminum coupling agent is expressed by the general formula and its chemical name is acetoalkoxyaluminum diisopropylate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a first magnetic layer in which magnetic powder is dispersed in a binder as a lower layer, on which a second magnetic layer in which magnetic powder is dispersed in a binder is laminated. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
It is widely used as a video tape, a backup data storage, a floppy disk, and the like, and its demand has been remarkably growing.

In particular, recently, high-density recording such as a shorter recording wavelength or a digital recording method has been actively studied, and the development of a magnetic recording medium having excellent electromagnetic conversion characteristics has been demanded.

[0004] As such a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is combined with a vinyl chloride-vinyl acetate copolymer, a polyester resin, a urethane resin, a polyurethane resin or the like organic binder (bonding). So-called coating-type magnetic recording media prepared by applying a magnetic coating material dispersed in a non-magnetic material) on a nonmagnetic support and drying the coating material are widely used.

[0005] In recent years, as recording wavelengths have become shorter and higher densities found in video tape recorders (VTRs) and the like, the electromagnetic conversion characteristics of magnetic recording media such as video tapes and audio tapes have been improved. Mirror surface, finer magnetic particles, and higher packing.

For example, in the case of a coating type video tape, various polar groups are introduced into a resin of a binder or various kinds of dispersion are carried out in a dispersion step in order to make a magnetic paint containing ultrafine ferromagnetic powder into a highly dispersed state. Or using a kneader.

The structure of the magnetic recording medium is also changed from the conventional single magnetic layer to a two-layer structure in which two magnetic layers are vertically stacked.
Various structures, such as a two-layer structure of a magnetic layer and a nonmagnetic layer, have been used depending on the purpose.

[0008]

While studies for improving various characteristics of the magnetic recording medium are proceeding as described above, cost reduction is also one of the important themes to be studied.
That is, the magnetic layer is made thinner or the back coat layer is omitted, but the most important thing is to use an inexpensive material.

However, in general, when an inexpensive material is used, there is a concern that the surface roughness of the magnetic layer may be deteriorated due to the effects of deterioration in dispersibility, deterioration of paint characteristics, and the like.

In determining the quality of the magnetic recording medium,
It goes without saying that the magnetic properties are improved by the high dispersion, but the state of contact with the magnetic head by making the surface of the coating film mirror-finished is also important.

However, it is not easy to obtain good characteristics by using many inexpensive materials with the conventional paint composition and mixing method.

As the recording wavelength becomes shorter, a coating film in which finer magnetic powder is highly dispersed is formed in the upper layer, and the lower layer is used to record a long-wavelength signal such as a chroma signal. Coating configurations have been devised to form higher filling coatings. However, when such a magnetic layer having a two-layer structure is employed, problems such as surface roughness of the coating film, reduction in coating speed, and reduction in productivity due to difficulty in the coating process occur.

One of the causes of these problems is the coating properties of the lower magnetic layer, and the state of application of the lower magnetic layer greatly affects the surface roughness of the coating film and the properties of the magnetic recording medium. This has a greater effect as the upper magnetic layer is made thinner.

Although such a problem can be improved by increasing the thickness of the coating film of the upper magnetic layer, this improvement method cannot be adopted for the purpose of cost reduction.

[0015] In order to solve these problems, the coating thickness is reduced,
In addition, it was necessary to develop a paint for the lower magnetic layer to supply a magnetic recording medium with high characteristics.

Accordingly, an object of the present invention is to improve the surface properties of a laminated magnetic layer such as a two-layer structure, to supply an inexpensive and high-performance magnetic recording medium, and to achieve high-speed coating and stabilization. It is in.

[0017]

As described above, in order to obtain a high-performance magnetic recording medium, high filling of ferromagnetic powder and mirror-finish of the coating film are indispensable.

What is important in achieving a mirror-finished coating film is the dispersion and rheology of the magnetic paint. As described in the publicly known literature, the surface roughness of the coating film is improved by making the pigment such as the ferromagnetic powder and the abrasive highly dispersed, but inexpensive materials are used to reduce costs. Consideration has been given to shortening the manufacturing time, etc., and it is very difficult to achieve high dispersion under these conditions.

Further, the speed of the application step of the magnetic paint causes deterioration of the surface roughness due to the properties of the paint. In the case of an extrusion coat which is effective for speeding up the coating process, streaks and uneven coating caused by the characteristics of the coating material increase significantly with the speeding up. The deterioration of the surface roughness is affected by the paint properties, especially the paint viscosity and wettability. As a method of improving the paint properties, it can be improved by lowering the solid content of the magnetic paint, but cannot be adopted because the filling ratio of the ferromagnetic powder is reduced, and as a result, the electromagnetic conversion characteristics are reduced. Therefore, there is a need to develop magnetic paints with high filling and low viscosity.

The present invention has been made in view of such circumstances, and has been made in consideration of the first problem in which a magnetic powder is dispersed in a binder.
In a magnetic recording medium in which a magnetic layer is a lower layer and a second magnetic layer in which a magnetic powder is dispersed in a binder is laminated thereon, an aluminum coupling agent is contained in at least the first magnetic layer. And a magnetic recording medium characterized by the following.

Also, the present invention provides a magnetic recording medium comprising a first magnetic layer in which magnetic powder is dispersed in a binder as a lower layer, and a second magnetic layer in which magnetic powder is dispersed in a binder laminated thereon. In manufacturing a recording medium, an aluminum coupling agent is added to a first magnetic paint for forming the first magnetic layer, and then the first magnetic paint is applied. The present invention also provides a method for manufacturing a magnetic recording medium, in which a second magnetic paint for forming the second magnetic layer is applied (wet multilayer coating).

According to the present invention, in a magnetic layer having a laminated structure, an aluminum coupling agent is internally added to a magnetic paint for forming at least a lower magnetic layer (first magnetic layer) to thereby improve the paint properties. It improves the surface properties of the coating film.

In the conventional coating design, a strong adsorption state between the ferromagnetic powder and the binder has been required in order to obtain high durability. In order to obtain this adsorption state, a large amount of polar groups have been introduced into the binder, or various dispersants have been added. Like the upper layer paint, the conventional lower magnetic layer paint has high dispersibility,
We have been studying paint compositions to achieve high durability. However, in an actual magnetic recording medium, it is mainly the upper magnetic layer (second magnetic layer) that contacts the recording / reproducing head that requires coating film durability.

What is required for the lower magnetic layer is more important the coating properties for obtaining a good surface roughness than the coating durability. In order to obtain such a lower magnetic layer, an aluminum coupling agent is added in the present invention.

That is, by adding the aluminum coupling agent to the lower magnetic layer, the coupling group (hydrophilic group) in the molecule is adsorbed on the surface of the magnetic powder, and the hydrophobic group of the aluminum coupling agent is combined with the binder. The good affinity also has the effect of filling the binder between the magnetic powders, which allows the coupling agent to function as a dispersant and improve the dispersibility of the magnetic powder.

As a result, due to the high dispersion of the magnetic powder, as shown in FIG. 1, even if the upper magnetic layer is made thinner, the surface thereof is smoothed, and the electromagnetic conversion characteristics of the magnetic recording medium are improved. Further, high-speed coating by wet multilayer coating such as a wet-on-wet method using a die coater or the like described later can be stably realized.

When the thickness (average thickness) of the upper magnetic layer is reduced to 1.0 μm or less, the self-demagnetization loss can be reduced, the output at a short wavelength is improved, and the overwrite characteristics are also improved. . However, the thickness of the magnetic layer is preferably 0.05 μm or more from the viewpoint of preventing deterioration of coating properties and electromagnetic conversion characteristics. Here, the thickness of the upper magnetic layer was determined for any 10 points of a cross-sectional photograph taken with a TEM (transmission electron microscope), and the average value was referred to as the above “average thickness”.
It is defined.

The amount of the above aluminum coupling agent is
It is desirable to use 0.5 to 5 parts by weight based on 100 parts by weight of the magnetic powder. In the present invention, a predetermined amount of the aluminum coupling agent may be added to the upper magnetic layer together with the lower magnetic layer.

When the content is more than 5 parts by weight,
Many unreacted functional groups with the binder remain in the lower magnetic layer,
Since these interact with each other, the dispersibility tends to decrease. On the other hand, when the content of the coupling agent is less than 0.5 parts by weight, it becomes difficult to function as a powder dispersant.

The aluminum coupling agent that can be used in the magnetic recording medium of the present invention and the method for producing the same has a hydrophilic group having an affinity for magnetic powder and a hydrophobic group having an affinity for a binder. The general formula is shown below, and specific examples are shown below.

[0031]

Embedded image (However, R ¹ —O is a hydrophilic group, R ¹ is an alkyl group or the like and may form a ring with Al, and R ² and R ³ are an alkyl group or the like and become a hydrophobic group.)

For example, R ¹ is an isopropyl group, R
^{When 2} is a methyl group, the above general formula can be expressed as follows.

Embedded image

The aluminum coupling agent used in the present invention is in a strong covalent bond state (adsorption form) with inorganic substances such as ferromagnetic powder. Titanate coupling agents are mentioned as substances having a similar effect, but aluminum coupling agents are excellent not only in magnetic powder but also in dispersion of pigments such as carbon black and titanium dioxide. In magnetic recording media, a large amount of carbon black has been added for the purpose of cost reduction and reduction of electric resistance, and the addition of an aluminum coupling agent is also effective in this regard. The bonding state as described above is the coating property of the magnetic coating,
In particular, the wettability is improved, which is very effective for applying a magnetic paint. However, it is desirable that the binding between the ferromagnetic powder and the binder is not hindered in order to maintain coating film durability.

Of course, the above-mentioned adsorption form can be improved by the combination of the polar group of the binder and the polar group of the aluminum coupling agent. However, in the present invention, since the coating properties of the lower magnetic layer are important, Unlike the case of the upper magnetic layer, the bonding between the ferromagnetic powder and the binder in the lower magnetic layer is not so important in the present invention.

Rather, in the present invention, it is desirable and possible to employ an inexpensive binder (ie, a binder containing a nonpolar group or a trace amount of a polar group) for cost reduction.

In the present invention, the magnetic paint used to form the magnetic layer is, in practice, a method in which an aluminum coupling agent is mixed with a ferromagnetic powder and a binder at the same time and kneaded and dispersed with a solvent, or Kneading the powder previously treated with an aluminum coupling agent together with a binder and a solvent,
It is prepared by a method of performing dispersion. In this case, the aluminum coupling agent is contained at least in the upper magnetic layer.

In the magnetic recording medium of the present invention, a binder, a ferromagnetic powder, a lubricant, an abrasive, an antistatic agent, a dispersant, a rust preventive, a carbon mixed into the magnetic layer, etc., mixed into the magnetic layer. As a solvent used for preparing a magnetic coating material on a non-magnetic support provided with a magnetic layer or a coating type magnetic recording medium, any of conventionally known solvents can be applied, and there is no particular limitation.

As the binder used for the upper and lower magnetic layers of the present invention, known materials can be used for both. That is, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Copolymer, acrylate-vinylidene chloride copolymer, acrylate-acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride , Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, phenolic resin, epoxy resin, Curable polyurethane resins, urea resins, melamine resins, alkyd resins, urea - formaldehyde resin,
Examples thereof include a polyvinyl acetal resin, a cellulose derivative, and a mixture thereof.

Further, polyurethane resins, polyester resins, acrylonitrile-
Cellulose derivatives, phenolic resins, epoxy resins, and the like, which are supposed to impart rigidity to butadiene copolymer and the like, are desirable. The above-mentioned binder may be one in which durability is improved by crosslinking an isocyanate compound, or an appropriate polar group is introduced.

Among the above-mentioned binders, the binder used in the present invention is not limited, but the binder having a Tg (glass transition point) of 50 to 120 ° C. for the first magnetic layer (lower layer) is used alone or Total Tg of 50 to 12 in combination of low Tg and high Tg
0 ° C., and the Tg of the binder in the second magnetic layer (upper layer) becomes 20.
It is desirable to use a material having a total Tg of 20 to 50 ° C alone or a combination of a low Tg and a high Tg.

Examples of the curing agent for the binder include aromatic polyisocyanates and aliphatic polyisocyanates.
These and active hydrogen adducts are preferred. As the aromatic polyisocyanate, toluene diisocyanate (TD
I) 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenyl diisocyanate, m
-Phenyl diisocyanate, 1,5-naphthyl diisocyanate, and the like. Further, examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, and cyclohexane diisocyanate. Active hydrogen compounds forming adducts with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane,
There are glycerin and the like, and the average molecular weight is 100 to 5,000.
Are preferred.

The ferromagnetic powder used in the present invention includes γ-FeOx (x = 1.33 to 1.5), Co-modified γ-FeOx (x = 1.33 to 1.5), Fe or N
Known materials such as a ferromagnetic alloy containing i or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used. In addition, these ferromagnetic powders include Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Se, Te, Ba, Ni, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, P, Mn, Zn, Co,
It may contain atoms such as Sr and B.

The lubricant used in the present invention includes silicone oil, fatty acid-modified silicone, fluorine-containing silicone or other fluorine-based lubricant, polyolefin, polyglycol, alkyl phosphate and metal salt, polyphenyl ether, alkyl fluoride. ether,
Alcohols having 12 to 24 carbon atoms (which may contain respective unsaturations or may be branched), and have 12 to 24 carbon atoms
And amine-based lubricants such as amine salts of alkyl carboxylic acids and amine salts of fluorinated alkyl carboxylic acids, and the like.

Specific examples of higher fatty acids and fatty acid esters include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid,
Linoleic acid, octyl stearate, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, heptyl stearate and the like. Further, the lubricant may be mixed with a plurality of lubricants.

Examples of the abrasive used in the present invention include α-alumina, β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, quartzite and garnet. Known materials having a Mohs' hardness of 6 or more containing garnet, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, or the like as a main component can be used alone or in combination.

The average particle size of these abrasives is from 0.01 to
Although 2 μm is preferable, abrasives having different particle sizes may be combined as needed, or a single abrasive may be used with a broad particle size distribution.

As carbon black (for example, as an antistatic agent) used in the magnetic layer of the present invention, known carbon black can be used. For example, acetylene black, furnace black, black for color and the like can be arbitrarily used. Further, in order to improve the handling during the manufacturing process, a granular material may be used. It is preferable to use carbon black having an average particle size in the range of 10 to 1000 nm.

The dispersing agents used in the upper magnetic coating composition of the present invention include metal soaps comprising fatty acids having 5 to 25 carbon atoms and their alkali metals or alkaline earth metals, fatty acid esters, fatty acid amides and amines, Known dispersants such as quaternary ammonium salts, phosphate esters, and borate esters can be used.

As the material of the nonmagnetic support used in the present invention, those generally used for magnetic recording media can be used, and polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyolefins such as polyethylene and polypropylene. , Cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamideimide, other plastics, metals such as aluminum and copper, and aluminum alloys , Light alloys such as titanium alloys, ceramics, single crystal silicon, and the like. The shape of the non-magnetic support (or the magnetic recording medium) may be various, such as a tape shape or a disk shape.

Solvents for preparing the magnetic paint of the present invention include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethyl acetate monoethyl ether and the like. Ester solvents, glycol monoethyl ethers, glycol ether solvents such as dioxane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, Chlorine-containing solvents such as chlorobenzene are exemplified. In addition, other conventionally known organic solvents can be used.

Known methods can be used for preparing the magnetic coating material of the present invention. For example, a roll mill, a ball mill, a sand mill, a tron mill, a high-speed stone mill, a basket mill, a disper, a homomixer, a kneader, a continuous kneader, an extruder, a homogenizer, an ultrasonic disperser, and the like can be used.

When preparing a magnetic paint, the magnetic particles and other additive particles may be separately dispersed and then mixed.

In the application of the magnetic paint, a pretreatment such as a corona discharge treatment or an electron beam irradiation treatment is performed on an undercoat layer such as an adhesive layer or on the nonmagnetic support before directly applying to the nonmagnetic support. No problem.

Further, a back coat layer made of carbon or a non-magnetic paint may be provided on the opposite side of the magnetic layer.

The method of coating on the nonmagnetic support of the present invention includes air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, gravure coat, transfer roll Examples of the method include a coating method and a cast coating method, and other methods are also possible. Further, simultaneous multilayer coating by extrusion coating may be used.

The magnetic recording medium of the present invention has a structure in which a first magnetic layer 4 and a second magnetic layer 2 are laminated on a nonmagnetic support 1 in this order, as shown in FIG. Further, the back coat layer 3 may be provided on the surface of the support opposite to the lamination surface like a virtual line, but this is not always necessary. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 3, the upper layer is further divided into layers 5 and 6, and the composition or physical properties of each layer are changed (for example, the specific surface area of the magnetic powder is changed).

In the magnetic recording medium shown in FIGS. 2 and 3, the thickness of the first magnetic layer 4 is 1.0 to 4.0 μm (for example, 1.5 to 4.0 μm).
μm), and the thickness of the second magnetic layer 2 or the total thickness of the magnetic layers 5 and 6 is set to 1.0 μm or less (for example, 0.5 μm).

As a preferred coating method, there is a multilayer coating using a wet-on-wet extrusion coating method (die coating).

FIG. 4A shows an example in which two coaters are used.
FIG. 4B shows an example in which one coater is used to discharge paint from separate slits, and FIG. 4C shows an example in which one coater is used to discharge each paint from a single slit.

In the coating apparatus shown in FIG. 4, for example, when the magnetic recording medium shown in FIG. 1 is manufactured, the extrusion type die coater 10, 11, or 10 is fed while feeding the supplied nonmagnetic support 1 in the direction of arrow D. Thus, the lower magnetic layer coating material 4a 'and the upper magnetic layer coating material 2a' are discharged to form two layers of a lower layer 4a and an upper layer 2a by a wet-on-wet method.

The die coater is provided with liquid reservoirs 6 and 7, and the paints 2a 'and 4a' are simultaneously overlapped by a wet-on-wet method.

In the multi-layer coating by the wet-on-wet method, the upper magnetic layer is applied while the lower magnetic layer is wet (undried), so that the surface of the lower layer (that is, the boundary surface with the upper layer) is formed. And the surface properties of the upper layer are improved, there is no need to consider the solvent resistance of the lower layer with respect to the paint of the upper layer, and the adhesion between the upper and lower layers is improved. In addition, the high-speed coating can be stably performed by improving the dispersibility by adding the aluminum coupling agent to the lower layer.

As a result, the performance required as a magnetic recording medium, which is required to have high output and low noise for high density recording, is satisfied, and film peeling is eliminated, and film strength is improved. In addition, dropout can be reduced, and reliability is improved.

The upper and lower layers formed by the wet-on-wet multi-layer coating method have a boundary region having a certain thickness and a mixture of components of both layers, except when a clear boundary substantially exists. Although it may be present, the upper or lower layer excluding such a boundary region is referred to as an upper magnetic layer,
The lower magnetic layer may be used. Either case is included in the scope of the present invention.

After the above-mentioned multi-layer coating, it is introduced into a drier and, if necessary, guided to a calender and wound up on a take-up roll. Further, after a back coat layer is applied to the opposite surface of the multilayer coating layer, a magnetic tape is formed by slitting the tape into, for example, an 8 mm width, and the magnetic tape is accommodated in a cassette to manufacture a tape cassette.

[0066]

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

In the following example, a dispersant (coupling agent)
Three types of lower layer magnetic paints were prepared without addition, with the addition of a silane coupling agent, and with the addition of an aluminum coupling agent. Changes in the paint properties and the tape properties when applying two layers were confirmed (samples # 2 to # 12). Upper single-layer coating (sample # 1) to confirm the superiority of the two-layer coating to the single-layer coating
A lower single-layer coating (sample # 13) for confirming the inability to add an aluminum coupling agent to the upper layer was also performed at the same time, and a comparison was made. In addition, no back coat was applied because the cost reduction was taken into account. In the following examples, “parts” means “parts by weight”.

According to the following composition, a magnetic paint for forming the upper magnetic layer was prepared. <Upper layer magnetic paint> After kneading the magnetic paint composition shown in the following Table 1 with a continuous kneader, it was dispersed using a sand mill,
Add 4 parts of polyisocyanate and 1 part of myristic acid, add 1 part
The solution was filtered through a filter having an average diameter of μm to obtain an upper layer magnetic coating liquid.

[0069]

A magnetic undercoat layer was prepared according to the following composition. <Lower layer magnetic paint> Using a dispersant (coupling agent) shown in Table 3 below, a magnetic paint composition shown in Table 2 below was kneaded in a continuous kneader, and then dispersed using a sand mill.
4 parts of polyisocyanate was added, and the mixture was filtered through a filter having an average diameter of 1 μm to obtain a lower magnetic coating liquid.

[0071]

The above upper or lower magnetic coating liquid was coated by extrusion coating on a polyethylene terephthalate film having a thickness of 14.0 μm to a thickness shown in Table 3, followed by drying, calendering and curing. The resulting wide magnetic film was cut into 1/2 inch widths to produce video tapes (Sample # 1, Sample # 13).

Similarly, the upper and lower magnetic coating liquids were applied to a 14.0 μm-thick polyethylene terephthalate film using an extrusion coater (simultaneous multilayer coating device) shown in FIG. 4A. Simultaneous application of lower layer with thickness shown in Table 3 (wet-on-wet method)
Then, the wide magnetic film obtained through the same post-process as the former was cut into イ ン チ inch width to produce video tapes (samples # 2 to # 12). In addition, a tape having the same composition as that of Sample # 10 except that it did not have a functional group (-COOH) as a binder of the lower magnetic coating liquid was also prepared (Sample # 14).

From the above, the following measurements were performed for each of the prepared video tapes. (1) Dispersibility The lower layer magnetic coating liquid and the upper layer magnetic coating liquid are applied on a polyethylene terephthalate film (14.0 μm thickness) at a coating thickness and dried, and then the glossiness (gloss) of the coated surface is obtained.
Is a digital variable-angle gloss meter “VG-1” manufactured by Nippon Denshoku Industries Co., Ltd.
D "at an incident angle of 45 °. Each glossiness was represented by the following evaluation criteria. ○ Gloss 120% or more △ Gloss 100% or more, less than 120% × Gloss less than 100%

(2) Viscosity of paint Regarding the lower layer magnetic paint liquid, a viscometer “DIGITA” manufactured by Tokyo Keiki Co., Ltd.
The load current value of the paint was measured by "L VISCOMETER DVM-B".

(3) Magnetostatic properties The prepared tape was measured at 20 ° C. and 50% RH using a VSM-P10-15auto, an ultra-high-vibration sample magnetometer dedicated to room temperature, manufactured by Toei Industry Co., Ltd. did.

(4) Film Thickness The total thickness of the magnetic recording medium was measured using “Modul units 403 and 372” manufactured by TESA, and the thickness was calculated by subtracting the thickness of the nonmagnetic support. Considering measurement errors, three points were measured and the average was taken as the coating thickness.

(5) Three-dimensional roughness The surface of the magnetic coating film and the surface of the non-magnetic support were measured using “ETB-30HK” manufactured by Kosaka Laboratory. The total average of the surface roughness is represented by SRa, the average of 10 points is represented by SRz, and the maximum value is represented by SRmax.

(6) RF-OUT (Video Output) A video signal was recorded using a VTR “AG-6200” manufactured by Matsushita Electric Industrial Co., Ltd., and the reproduction level was set using sample # 1 as a reference tape. It is represented by a relative value when 0 dB is set.

(7) YS / N (Video S / N) The S / N ratio of the video signal is represented by a relative value when the reference tape is set to 0 dB.

(8) C-OUT (Chroma Output) A chroma signal is recorded and reproduced, and the reproduced output level is represented by a relative value when the reference tape is set to 0 dB.

(9) CS / N (Chroma S / N) The S / N ratio of the chroma signal is represented by a relative value when the reference tape is set to 0 dB.

(10) Still Characteristics Using a VTR “AG-6200” manufactured by Matsushita Electric Industrial Co., Ltd., the durability of the coating film in a pause state during reproduction was confirmed.
Each durability time is represented by the following evaluation criteria. ○ Endurance time is 120 minutes or more △ Endurance time is 60 minutes or more and less than 120 minutes × Endurance time is less than 60 minutes

(11) Clog Characteristics Using a VTR “AG-6200” manufactured by Matsushita Electric Industrial Co., Ltd., the clogged state of the head gap due to the effect of powder drop during reproduction running was evaluated. Each head state is represented by the following evaluation criteria. ○ Clogged state No powder dropout △ Clogged state Powder dropout is observed but no problem in recording / reproduction × Clogged state Head gap is clogged due to powder dropout and recording / reproduction is not possible

The results of the above measurements are shown in Table 3 below.

[0086]

[Table 1]

[0087]

[Table 2]

As shown in Table 3, according to the present invention, by adding a predetermined amount (particularly 0.5 to 5 parts by weight) of an aluminum coupling agent to the coating composition of the lower magnetic layer,
The paint properties have been improved and various properties have been improved (samples # 8-12, especially samples # 9-11).

The most effective effect is obtained on the surface roughness of the coating film, which is much better than that of a two-layer coating film of another composition, and is equal to or higher than that of a single-layer coating film. It is considered that the major factor of the property deterioration in other compositions is that the property deterioration of the lower coating material lowers the surface roughness of the lower magnetic layer, and the affected upper magnetic layer also lowers the surface roughness.

Further, when a large amount of carbon black was added to the lower magnetic coating material, the dispersion was significantly reduced.
The effect of the aluminum coupling agent on improvement in this respect is apparent.

As described above, the aluminum coupling agent which enables high dispersion and makes the coating film mirror-finished, however, has a problem when added to the upper layer. In the sample # 13, a single-layer coating of only the lower magnetic coating film was performed. Some of the coatings are effective for improving the magnetostatic characteristics and electromagnetic conversion characteristics, but have an adverse effect on the film durability.

In the case of a two-layer coating film, since the lower layer does not directly contact the recording / reproducing head, there is no major problem because durability is not so required. In addition, even if a binder having no functional group is used as the binder of the lower magnetic layer as in sample # 14, the result is good.

In the two-layer coating film according to the present invention,
FIG. 1 shows the change in the characteristics (for example, surface roughness SRa and RF-OUT) depending on the amount of the aluminum coupling agent added to the lower layer. However, when the amount is 0.5 to 5 parts by weight, the result is further improved. I understand.

As described above, according to the present invention, by adding an aluminum coupling agent to the lower magnetic layer, the coating properties are improved, the surface roughness is improved, and the magnetic recording medium having excellent electromagnetic conversion properties is obtained. Could be obtained.

Specifically, the aluminum coupling agent added to the lower magnetic coating material is firmly bound on the surface of the ferromagnetic powder, and inhibits the binding between the binder and the ferromagnetic powder. The direction of the conventional ferromagnetic powder and binder is completely opposite to the direction in which they are bonded firmly to obtain durability. Absent.

The effect of the addition of a small amount of the aluminum coupling agent is not clear. When added in a large amount, the plasticization of the lower magnetic coating film proceeds, and problems such as adhesion to the non-magnetic support arise. As a result, the addition of about 0.5 to 5 parts by weight is effective for improving the paint properties and the surface roughness. With the addition of the above-mentioned aluminum coupling agent, the durability of the lower coating film itself tends to deteriorate, but what is required for the lower magnetic layer is a coating property for obtaining a good surface roughness, and a dispersion property. It is also possible to realize high filling by improving the performance.

The aluminum coupling agent is effective for various binders, and it is possible to use an inexpensive material such as a binder having a small amount of a polar group or a nonpolar group. If an inexpensive material can be used for the lower magnetic layer that occupies the majority of the coating film, the cost reduction effect will be significant.

As described above, according to the present invention, when the lower magnetic layer to which the aluminum coupling agent is added is used,
A magnetic recording medium capable of high-quality recording and reproduction can be provided.

[0099]

As described above, according to the present invention, since at least the magnetic layer contains an aluminum coupling agent, the coating characteristics are improved, the surface roughness is improved, the electromagnetic conversion characteristics are excellent, and the high speed is achieved. It is possible to obtain a magnetic recording medium capable of performing coating stably. Further, the aluminum coupling agent is effective for various binders, and it is possible to use an inexpensive material such as a binder having a small amount of a polar group or a nonpolar group. If an inexpensive material can be used for the lower magnetic layer that occupies the majority of the coating film, the cost reduction effect will be significant.

As described above, according to the present invention, when the lower magnetic layer to which the aluminum coupling agent is added is used,
It is possible to provide a magnetic recording medium capable of performing high-quality recording and reproduction and stably performing high-speed coating.

[Brief description of the drawings]

FIG. 1 is a graph showing changes in surface roughness and reproduction output depending on the amount of an aluminum coupling agent added to a lower magnetic layer in a magnetic recording medium according to the present invention.

FIG. 2 is a sectional view of an example of a magnetic recording medium according to the present invention.

FIG. 3 is a sectional view of another example of the magnetic recording medium according to the present invention.

FIG. 4 is a schematic view of a die coat coating apparatus that can be used for forming an upper magnetic layer and a lower magnetic layer of a magnetic recording medium according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Non-magnetic support, 2 ... Upper magnetic layer, 2a ', 4a' ...
Paint (coating), 3 ... back coat layer, 4 ... lower magnetic layer

Claims (8)

[Claims] 1. A magnetic recording medium comprising a first magnetic layer in which a magnetic powder is dispersed in a binder as a lower layer, and a second magnetic layer in which a magnetic powder is dispersed in a binder laminated thereon.
A magnetic recording medium, characterized in that at least the first magnetic layer contains an aluminum coupling agent. 2. The magnetic recording medium according to claim 1, wherein the aluminum coupling agent is contained in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the magnetic powder. 3. The magnetic recording medium according to claim 1, wherein only the first magnetic layer contains the aluminum coupling agent. 4. The aluminum coupling agent has a hydrophilic group having an affinity for the magnetic powder and a hydrophobic group having an affinity for the binder.
2. The magnetic recording medium described in 1. above. 5. A magnetic recording medium in which a first magnetic layer in which a magnetic powder is dispersed in a binder is used as a lower layer, and a second magnetic layer in which a magnetic powder is dispersed in a binder is laminated thereon. At this time, an aluminum coupling agent is added to a first magnetic paint for forming the first magnetic layer,
A method for manufacturing a magnetic recording medium, comprising applying a magnetic paint and applying a second magnetic paint for forming the second magnetic layer while the applied layer is in an undried state. 6. The method according to claim 5, wherein the aluminum coupling agent is added in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the magnetic powder. 7. The method for producing a magnetic recording medium according to claim 5, wherein the aluminum coupling agent is added only to the first magnetic paint. 8. An aluminum coupling agent having a hydrophilic group having an affinity for the magnetic powder and a hydrophobic group having an affinity for the binder as the aluminum coupling agent. Item 6. The method for manufacturing a magnetic recording medium according to Item 5.