JPH03165312A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic conversion characteristic of the medium by forming the magnetic layer with the uppermost layer and at least one lower layer and adding specified pts.wt. of alumina particles to 100 pts.wt. of the magnetic powder in the uppermost layer. CONSTITUTION:The magnetic layer of the magnetic recording layer provided on a nonmagnetic substrate is formed with the uppermost layer and at least one lower layer, 3-15 pts.wt. of alumina particles having <=0.4mum average diameter and which have been separately dispersed is added to 100 pts.wt of the magnetic powder in the uppermost layer, and <=10 pts.wt. of nonmagnetic oxide particles having <=0.4 mum average diameter and which have been separately dispersed to 100 pts.wt. of the magnetic powder in at least one lower layer. The thickness of the first magnetic layer 2 is preferably controlled to 1.5-4.0 mum, and the thickness of the second magnetic layer 4 or the total thickness of the second and third magnetic layers 5 and 6 to<=1.0mum. As a result, the effect on the surface property of the uppermost layer is reduced, and the electromagnetic conversion characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

In magnetic recording media having a single magnetic layer, there is an increasing demand for high-density recording, and efforts are being made to make the ferromagnetic powder finer and to smoothen the surface of the magnetic layer. As the ferromagnetic powder becomes finer and the surface of the magnetic layer becomes smoother, the electromagnetic conversion characteristics of a magnetic recording medium using the same improve, but this becomes disadvantageous in terms of running durability. That is, friction increases at the contact portion between the magnetic head, guide post, rotary head cylinder, etc. and the magnetic layer, scratches occur on the surface of the magnetic layer, or ferromagnetic powder easily falls off from the magnetic layer. Therefore, there is a problem that dropout is likely to occur. Furthermore, if the running durability of the magnetic layer is low, the life span (still life) of the magnetic layer will be reduced, particularly under conditions in which still images are continuously reproduced (still mode).

In order to improve the running durability of a magnetic recording medium using such finely divided ferromagnetic powder, we added Crz to the magnetic layer.
o, , Al2O:l, Ti0z, Sio2, and other abrasives are added (Japanese Patent Application Laid-Open No. 64-37717,
No. 61-283030, No. 53-133406, No. 5755973, No. 61-57036).

However, when adding an abrasive in this way,
It is difficult to select the amount of abrasive added and the particle size. For example, if too much abrasive is added, the running durability of the magnetic layer will improve, but the contact property of the magnetic layer with the magnetic head will decrease, resulting in electromagnetic conversion. The properties deteriorate, and on the other hand, if the amount added is small, sufficient durability cannot be obtained. Regarding the particle size of the abrasive, if the particle size is small, the amount of head wear will be small but the still characteristics will be poor; if the particle size is large, the still characteristics will be improved but the amount of head wear will be increased. For this reason, in conventional single magnetic layer magnetic recording media, an abrasive with an appropriate particle size was used to achieve a balance between head wear and still characteristics. cannot be satisfied.

On the other hand, in magnetic recording media, especially video magnetic recording media that require short wavelength recording, it is necessary to increase the magnetic recording capacity or to improve and balance the magnetic recording characteristics of the medium in both the high frequency range and the low frequency range. Therefore, a medium having multiple magnetic layers has been proposed (Japanese Patent Laid-Open No. 48-98803).
No., JP-A-59-172142, JP-A-52-221
No. 8, JP-A-51-64901, JP-A-56-12
No. 937, JP-A-63-146211, JP-A-60-
47228, etc.). According to these known techniques,
It is designed to use relatively fine particles of magnetic powder in the upper layer of the magnetic layer and larger magnetic powder in the lower layer, so that the upper layer receives the video output and the lower layer receives the chroma audio output.

In such a magnetic recording medium having multiple magnetic layers, the upper layer is thinner than the lower layer (usually 0.6 to 1 μm for the upper layer and 1.5 μm for the lower layer), which is completely different from the case of the single layer described above.
4 μm), therefore, addition of abrasives cannot be considered as in the case of a single magnetic layer. For example, JP-A-63-44
In Publication No. 6211 and Japanese Patent Application Laid-open No. 60-47228,
It has been shown to contain an abrasive in both the upper and lower layers of the magnetic layer, that is, to add 1 part by weight or 2 parts by weight of alumina to 100 parts by weight of magnetic powder in the upper and lower layers, respectively. However, in all of these methods, the polishing force of the magnetic layer is weak and the surface is smooth, so they are insufficient to reduce the sliding noise generated when sliding in contact with the magnetic head, and to increase still durability and RF output. It turned out to be.

This seems to be due to not only the quantitative problem of alumina, but also special problems that cannot be predicted with a single magnetic layer, such as the extremely thin upper layer of the b'A layer. The bulletin does not mention any countermeasures.

For all conventional media, it is necessary to form the upper magnetic layer with good surface properties in consideration of the influence of the lower magnetic layer, or to obtain high output and high S/N by adjusting the surface properties of the medium. In determining the correlation between the coating conditions of the upper and lower magnetic layers, sufficient conditions have not yet been found. As a result, if the surface of the medium is too mirror-finished, sliding noise will be large during its running, and if the surface of the medium is rough, the electromagnetic conversion characteristics will be degraded. In particular, depending on the particle size and amount of the abrasive, its dispersibility becomes poor and the amount present on the surface of the magnetic layer decreases. Therefore, in order to distribute the required amount of abrasive on the surface, the amount must be increased. Therefore, the electromagnetic conversion characteristics will deteriorate.

C.1 Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium having a plurality of magnetic layers while exhibiting good electromagnetic conversion characteristics.
The objective is to improve running durability, reduce head wear and head scratches, and further improve the durability of still characteristics in still mode, greatly reducing dropouts, head clouding, and sliding noise.

22. According to the present invention, the magnetic layer provided on the non-magnetic support is composed of an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer has an average particle diameter of 0.4 μm or less. The magnetic powder 1 in the uppermost layer has alumina particles separately dispersed therein.
0.00 parts by weight, and in at least one layer of the lower layer, non-magnetic oxide particles having an average particle size of 0.4 μm or less are separately dispersed in the at least one layer. This relates to a magnetic recording medium in which 10 parts by weight or less (however, if added to the lower layer of multiple layers, 10 parts by weight or less for each layer) is added to 100 parts by weight of the magnetic powder.

In the magnetic recording medium of the present invention, since the magnetic layer is composed of a plurality of layers (the uppermost layer and at least the lower IN layer), the upper layer has good high-frequency recording and reproduction characteristics such as video output, and Each layer can be formed so that relatively low-frequency recording and reproduction characteristics such as chroma and audio output are improved in the lower layer. For this purpose, it is generally necessary that the coercive force (Hc) of the upper layer (especially the top layer) be larger than that of the lower layer, and that the film thickness (or layer thickness) of the upper layer be thin, especially 1.0μ.
It is desirable that it be less than m. Further, it is desirable that the thickness of the lower layer adjacent to this upper layer is 1.5 to 4.0 μm.

In the present invention, it is desirable that the plurality of layers constituting the magnetic layer are adjacent to each other. The above-mentioned lower layer may be one layer, or may be two or more layers, but at least one of these layers (especially the lower layer adjacent to the top layer) and/or the top layer , add the carbon black paste described above. However, in addition to the case where there is substantially a clear boundary between each layer, there may be a case where there is a boundary area where magnetic powder from both layers coexists at a certain thickness.
The upper or lower layer excluding these boundary areas is referred to as each of the above layers. In particular, the medium of the present invention is suitable for forming each magnetic layer by wet-on-wet coating. Of course, an et-on-dry method may also be used, in which the upper layer is applied after drying the lower layer.

In the present invention, the uppermost layer contains alumina (especially α-alumina) particles with excellent abrasive power in a specific particle size (0.4 μm or less) and in a specific ratio (3 to 15 parts by weight per 100 parts by weight of magnetic powder). ), but what should be noted here is that alumina is not simply contained in the top layer, but the particle size and amount of alumina mentioned above and other constituent requirements of the present invention (
By combining the particles (particle size and amount of the non-magnetic oxide particles in the lower layer), a synergistic effect is realized, which reduces head wear, sliding noise, head cloudiness, dropout, and improves electromagnetic conversion characteristics. This is completely achievable.

That is, in the case of a plurality of magnetic layers as in the present invention, it is surprising that, based on the present invention, unless the abrasive (alumina) contained in the uppermost layer is increased to 3 parts by weight or more, the surface of the uppermost layer is Since the surface tends to become too smooth, it is not possible to obtain an appropriate surface quality of the upper layer, and its polishing power is also insufficient. However, by setting the abrasive content to 3 parts by weight or more (especially preferably 3 parts by weight or more) as in the present invention, dropouts, head cloudiness, and sliding noise can be greatly reduced while improving electromagnetic conversion performance. It is possible to do so. Since the top layer is thin, the amount of abrasive per unit volume (thickness) is sufficient and the polishing effect can be enhanced. However, 15
The amount of abrasive should be 15 parts by weight or less, because if it exceeds 15 parts by weight, the amount will be too high and will actually deteriorate the electromagnetic properties, film strength, and hem wear. A more preferable range is 2 to 10 parts by weight. The average particle size of the alumina in this top layer should be 0.4 μm or less, but if the particle size exceeds 0.4 μm, it is too large and the electromagnetic conversion characteristics (
Lumi S/N, etc.) deteriorates. This average particle size is 0.10~
0.30 am is good, 0.18-0.25 pm
is even better.

In combination with this top layer abrasive solvent, at least one lower layer contains non-magnetic oxide particles (α-alumina, chromium oxide (Cr203),
silica, a-FezOz, Tie, zirconia, etc.)
It is also important that 10 parts by weight or less of is contained per 100 parts by weight of magnetic powder. Here, the average particle size is 0.4
The reason for setting it below μm (preferably 0.10 to 0.30 μm, more preferably 0.18 to 0.25 μm) is the same as above, but the smaller the amount, the better the surface properties of the top layer. Since there are fewer shadows and the electromagnetic conversion characteristics are improved, 10
It should be less than 2.0 parts by weight, preferably 2.0 to 8.5 parts by weight, and even better 2.5 to 8.0 parts by weight. The amount of the non-magnetic oxide (abrasive) particles added to the lower layer is 10 parts by weight or less for each layer when the lower layer is a plurality of layers.

In addition, in the present invention, the above-mentioned "average particle diameter j" refers to the average value of the long axis length per 100 abrasive particles (hereinafter,
similar).

Another feature is that an abrasive paint in which abrasive particles are separately dispersed (particularly pre-dispersed in a binder resin) is added to the magnetic paint, rather than being coated with a cloth. In other words, by this separate dispersion, the dispersion of the abrasive can be sufficiently improved compared to the case where the powder is directly dispersed, so that the desired abrasive power can be achieved while maintaining good electromagnetic conversion characteristics. Can be done.

Suitable binder resins used to prepare such abrasive paints contain inphorone diisocyanate as an isocyanate component, and preferably contain polar groups such as sulfonic acid groups and/or salts thereof. It is a polyurethane. Alternatively, it is preferably a polyester containing a polar group such as the above-mentioned sulfonic acid group and/or a salt thereof.

Polyurethane containing such sulfonate groups, etc., especially polyester polyurethane, is a dicarboxylic acid that is the starting material for the polyester containing sulfonate groups, etc., and a dicarboxylic acid that does not contain sulfonate groups, etc. and diol, and diisocyanate (
In particular, it can be obtained by a condensation reaction and an addition reaction using isophorone diisocyanate). In the case of polyurethane, for example, a sulfonate group or the like can be introduced into a diol and a urethane resin can be synthesized in the same manner.

In the case of polyester, it can be synthesized by subjecting the above dicarboxylic acid and diol to a condensation reaction. In addition, as a binder resin, for example, nitrocellulose,
It can also be selected from among the condensing agents described below, such as polyvinyl chloride.

Polar groups such as the above sulfonate groups are -3O,M, -
Hydrophilic properties such as COOM, -PO(OM') 2 (where M is hydrogen or an alkali metal such as lithium, potassium, and sodium, and M' is a hydrocarbon residue or an alkali metal such as hydrogen, lithium, potassium, and sodium) It can be expressed as a polar group. These polar groups improve the compatibility between the abrasive paint and the magnetic powder, which further improves mutual dispersibility and prevents agglomeration of the abrasive, further improving coating liquid stability. Furthermore, the durability of the medium can also be improved.

Note that a method of modifying polyester, polyurethane, or vinyl chloride resin to introduce a polar group may also be considered.

That is, these resins and e.g. (1-CH2CH2sot M.

C1-CHt CH2030,M, (OM') Cj2-CH2-P-(OM'), 1 (However, in the formula, M and M' have the same meanings as above.

This is a method in which the above-mentioned polar group and a compound containing chlorine are condensed and introduced into the molecule by a dehydrochloric acid reaction.

The above carboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 15-naphthalic acid; aromatic oxycarboxylic acids such as p-oxybenzoic acid and P-(hydroxyethoxy)benzoic acid; Acids: Examples include aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid, and tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid. Among these, preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid. Examples of the dicarboxylic acid component containing the sulfonic acid metal salt group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

Examples of the diol component include ethylene glycol, propylene glycol, II 3-propanediol, 1,4-butanediol, ■,5-bentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2
．． 21 trimethyl-1,3-neobentanediol, 1
, 4-cyclohexane dimetatool, bisphenol A
Examples include ethylene oxide adducts of hydrogenated bisphenol A, ethylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and/or tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol can also be used in combination.

Examples of the above-mentioned isocyanate components used to obtain the polyurecne resin include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, P-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, and hexane diisocyanate. Methylene diisocyanate, tetramethylene diisocyanate, 3゜3'-dimethoxy-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,3-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1 .3-diisocyanatemethylcyclohexane, 14-diisocyanatemethylcyclohexane, 44' diisocyanate dicyclohexane, 44'
Examples include diisocyanate dicyclohexylmethane and isophorone diisocyanate.

The abrasive paint obtained by the above-mentioned separate dispersion may be in the form of a paste, but the amount of resin per 100 parts by weight of the abrasive is 5.
-25 parts by weight is good, and more preferably 10-20 parts by weight. In this separate dispersion method, the abrasive particles and the binder are mixed with an organic solvent at a high viscosity in the front, and then an organic solvent is added to disperse them at a low viscosity. Front line methods include three roll mills, two roll mills, pressure kneaders, AT kneaders, oven kneaders, Warner kneaders, etc., and low viscosity dispersion methods include sand mills, ball mills,
There are things like Lend Devil.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
Non-magnetic support 1 made of polyethylene terephthalate etc.
A first magnetic layer 2 and a second magnetic layer 4 are laminated thereon in this order. Further, although a back coat layer 3 is provided on the support surface opposite to the laminated surface, this need not necessarily be provided. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into layers 5 and 6.

In the magnetic recording medium shown in FIGS. 1 and 2, the thickness of the first magnetic layer 2 is preferably 1.5 to 4.0 μm,
Thickness of the second magnetic layer 4 or the second and third magnetic layers 5.6
The total film thickness is preferably 1.0 μm or less (for example, 0.6 μm).

The magnetic layer 2.4.5.6 may contain magnetic powder, but
Such magnetic powders include 7-Fe, 03CO-containing 1-
Fez O,, Fe50. , Co-containing Fe, iron oxide magnetic powder such as 04; Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Ni alloy, FeA2 alloy, Fe-Aj2-N
i alloy, Fe-A/2Co alloy, Fe Mn Zn
Alloy, Fe-NiZn alloy, Fe-Aj2-N 1-
Co alloy, FeAl-Ni-Cr alloy, Fe-Af-C
o-Cr alloy, Fe-Co-Ni-Cr alloy, Fe-C
.

Examples include various ferromagnetic powders such as NiP alloy, CoNi alloy, and other metal magnetic powders containing Fe, Ni, CO, etc. as main components. The outermost magnetic layer 4.6 and the other magnetic layers 2.5 (and/
Or 2), based on the present invention, the former 4.6 is the top layer and the latter 2.5 or 5 and 2 are the lower layers.

Among these magnetic powders, one suitable for each of the above-mentioned magnetic layers 2.4 can be selected. For example, if the upper layer 4 is made of a material having a higher quarry power (Hc) than the lower layer 2, a higher output medium can be obtained.

Also present in each magnetic layer is a lubricant (e.g. silicone oil,
Graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 2 carbon atoms (for example, stearic acid), fatty acid esters having 13 to 40 carbon atoms, and the like may be added.

The binder that can be used for the outer layer 2.4.5.6 preferably has an average molecular weight of about 10,000 to 200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, etc. Polymer, vinyl chloride-acrylonitrile copolymer, polyvinyl chloride, urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propione) -1-, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, various synthetic rubbers, phenolic resins, epoxy resins, urea resins, melamine resins,
Phenoxy resins, silicone resins, acrylic reactive resins, mixtures of isonianate prebolimers on high molecular weight polyester resins, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

It is desirable that these binders have the above-mentioned hydrophilic polar group from the viewpoint of dispersibility of the magnetic powder.

Further, when providing the puncture coat layer 3, the above-described binder contains non-magnetic particles such as barium sulfate and is applied to the back surface of the support.

Further, as the material of the support body 1 mentioned above, plastics such as polyethylene terephthalate and polypcobylene, A!
, metals such as Zn, glass, BN, Si carbide, ceramics such as porcelain, ceramics, etc. are used.

Next, FIG. 3 shows an example of the above-mentioned medium manufacturing apparatus.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, the film-like support 1 fed out from the supply roll 32 is coated with each of the above-mentioned paints for the magnetic layer 2.4 by an extrusion coater 10.11. After that, for example 2000G
It is oriented by a front-stage orientation magnet 33 of Gauss, and further introduced into a dryer 34 equipped with a rear-stage orientation magnet 35 of, for example, 2000 Gauss, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coated layer is led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered and then wound onto a winding roll 39.

Each paint may be fed to extrusion coater 10.11 through an in-line mixer (not shown). In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. Each extruded coke 10.11 has a liquid reservoir 13.1.
4 is provided to wet-on the paint from each coater.
Layer using the wet method. To manufacture the media shown in Figure 2,
In FIG. 3, one more extrusion coater may be added.

E, Example The present invention will be explained in detail below.

The components, proportions, mulberry planting order, etc. shown below may be changed in various ways without departing from the spirit of the present invention. In addition, in the following examples, "parts J" are all parts by weight.

first, Table below Each composition shown in 1. Reader, Knead in a sand mill, dispersed, Each magnetic paint was prepared.

Note) In the above, 0 -Fe2 3 means Co-containing (or deposited) Tez 3 PVC copolymer is vinyl chloride-vinyl acetate copolymer (VA
GH: U, C, C, manufactured by), polyurethane is tJR83
00 (sodium sulfonate-containing polyurethane manufactured by Toyobo Co., Ltd.), the non-magnetic metal oxide is a polyurethane resin (including isophorone diisocyanate) when based on the present invention,
and those containing sodium sulfonate such as UR8300 (above), or those added as a paste made by pre-dispersing (separately dispersing) in aromatic polyester diol, and the polyisocyanate is Coronate (manufactured by Nippon Polyurethane Co., Ltd.). be.

Each of the above-mentioned magnetic paints was discharged using the extrusion coater shown in FIG. 3 onto a polyethylene terephthalate base having a thickness of 14 μm, with the top layer having a thickness of 0.3 μm and the bottom layer having a thickness of 2.5 μm.
After coating to a dry thickness of 5 μm, orientation and drying treatment, supercalender treatment was performed. Thereafter, a back coat paint having the following composition was applied to the opposite side of the magnetic layer to a dry thickness of 1.0 μm.

Carbon black (average particle size 20 mμ) 40 parts Carbon black (average particle size 300 mμ) 5 parts Nitrocellulose 25 parts (Seltsuba BTHy2 manufactured by Asahi Kasei Co., Ltd.) N-2301 (manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Koro 2-
1-L (manufactured by Nippon Polyurethane Co., Ltd.) 10 parts cyclohexanone 400 parts methyl ethyl ketone 250 parts toluene
250 copies of a wide magnetic film was thus obtained and wound up. This film is A
Each videotape was cut into inch width pieces. The following performance evaluations were performed on each of these tapes, and the results are shown in Table 2.

(1) Head cloudiness was measured according to the following procedures.

■ Before measurement, clean the head to ensure that there is no cloudy head.

■ Add a single frequency of 6MHz to the sample tape (No. 1) (unused) by 20% compared to the reference tape.
After recording for 10 minutes at the recording level of
A single frequency of Hz is recorded for 2 minutes at a recording level of +20% relative to the reference tape.

■ At room temperature and low humidity (20%), sample tape (
No. 2) <Unused> Run in SP mode while recording the video signal from the beginning of winding to the end of winding.

■ Record the single frequency of 8MH2 again for 2 minutes on the sample tape (Nα1) at the same recording level as ■, and play it back.

<evaluation> ◎...There is no deposit on the glass part of the head.

○: Some of the deposits are present.

x: Adhesives are present on the entire surface of the head.

(2) Sliding noise was measured in the following manner.

■ Play back the tape without running it, and measure the system noise with a spectrum analyzer.

■ Play the sample tape 10 times for 1 minute each and measure the sliding noise with a spectrum analyzer.

(8M) [Based on the nozzle level near z based on the system noise: 1 (OdB), read the noise value of 10 passes.

(3) Electromagnetic conversion characteristics are Lumi-3/N, Chroma-3/N
About Video Deck rHR-37000J (J■
(manufactured by Company C), and Shibatsu R92 as a noise meter.
5 D-'. The frequencies of each signal are as follows.

Lumi-3/N: 6MHz R07-3/N: 629 KHz (4) Dropout is r HR-57000J
The number of dropouts of 100% white signal (1
The 1-minute average value of 5 μs, -14 dB) was measured using a VHOIBZ dropout counter (VHOIBZ).

(Left below) According to the results, based on the present invention, by adding an abrasive to the uppermost layer and the lower layer of the magnetic layer, Lumi-3/
It is good in all aspects including electromagnetic conversion characteristics such as N, running durability, (cloudy head, dropouts), and sliding noise.

This is because α-alumina with a predetermined particle size and amount is added as a separate dispersion to the top layer, and non-magnetic metal oxide is added with a predetermined particle size and amount as a separate dispersion to layers other than the top layer (tape This is thought to be due to the synergistic effect of improving the physical properties of the rubber and improving the head contact.

Next, when the magnetic layer is made up of three layers, layers 2, 5, and 6, as shown in Figure 2 (however, the upper layer 6 is the same as 4 in Figure 1, but the film thickness is 0.38 m1, and the middle layer is H between 2 and 4 in Figure 1
c (8500e), the film thickness is 0.3 μm, and the lower layer 2 is the same as 2 in Figure 1), and the performance evaluation was performed in the same manner as above.
The results shown in Table 3 below were obtained. According to this, it can be seen that, as in the case of two layers, the configuration of the present invention provides sufficient performance.

F1 Functions and Effects of the Invention As described above, the present invention has a structure in which the uppermost layer of the magnetic layer has an average grain size of 0.
．． Since 3 to 15 parts by weight of alumina with a diameter of 4 μm or less is added to the magnetic powder, dropouts, head cloudiness, and sliding noise can be greatly reduced while improving electromagnetic conversion performance, and head wear can also be reduced. Moreover, since the lower layer contains non-magnetic oxide particles with an average particle size of 0.4 μm or less in an amount of 10 parts by weight or less based on the magnetic powder, the effect on the surface properties of the top layer is reduced and the electromagnetic conversion characteristics are improved. .

[Brief explanation of the drawing]

The drawings are for illustratively explaining the present invention, and FIGS. 1 and 2 are cross-sectional views of an example of a magnetic recording medium, and FIG. 3 is a schematic diagram of an apparatus for manufacturing a magnetic recording medium. In addition, in the reference numerals shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 3...Back coat layer 4. 6... Upper magnetic layer 5... Intermediate magnetic layer.

Claims (1)

[Claims] 1. A state in which the magnetic layer provided on the non-magnetic support is composed of an uppermost layer and a lower layer consisting of at least one layer, and alumina particles having an average particle size of 0.4 μm or less are separately dispersed in the uppermost layer. 3 to 15 parts by weight are added to 100 parts by weight of the magnetic powder in the uppermost layer, and non-magnetic oxide particles having an average particle size of 0.4 μm or less are separately dispersed in at least one of the lower layers. 10 parts by weight or less (however, when added to the lower layer of multiple layers, 10 parts by weight or less for each layer) is added to 100 parts by weight of the magnetic powder in at least one layer.