JPH0442430A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain flat and high electromagnetic conversion characteristics from a low range to high range while reducing noise by successively forming first, second, and third magnetic layers on a nonmagnetic supporting body and specifying Hc (coercive force) of the ferromagnetic powder for each magnetic layer. CONSTITUTION:Three magnetic layers, namely, the first magnetic layer 1, second magnetic layer 2, and third magnetic layer 3 are formed on a nonmagnetic supporting body S to constitute this magnetic recording medium. The boundary between the first magnetic layer and the second magnetic layer, and the boundary between the second magnetic layer and third magnetic layer are clear and flat. Hc of the ferromagnetic powder to be incorporated into the first magnetic layer 1 is 500 - 800Oe, while Hc of the ferromagnetic powder to be incorporated in the third magnetic layer 3 is 800 - 1,100Oe. The ferromagnetic powder to be incorporated in the second magnetic layer 2 is a mixture powder of ferromagnetic powder having 500 - 800Oe Hc and ferromagnetic powder having 800 - 1,100Oe Hc. Thereby, the obtd. magnetic recording medium has flat and high electromagnetic conversion characteristics from a low range to high range with reduced noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium that has flat and high electromagnetic conversion characteristics from low to high frequencies.

[Prior art and inventions or assignments to be solved] Magnetic recording media such as audio tapes and video tapes have flat and high electromagnetic variation from low to high frequencies! ! ! ! In order to exhibit the characteristics, a technique is known in which a mixing region is provided between a single magnetic layer in which both components change continuously (Japanese Patent Application Laid-open No. 6
3-241721).

However, in this type of magnetic recording medium, the boundary between the mixed region and the magnetic layers sandwiching the mixed region is unclear, so that noise is likely to occur.

The present invention has been made to improve the above-mentioned situation.

That is, one object of the present invention is to reduce noise while
The object of the present invention is to provide a magnetic recording medium having flat and high electromagnetic conversion characteristics from low to high frequencies.

[Means for Solving the Problems] The present invention for achieving the above objects provides a magnetic material in which a first magnetic layer, a second magnetic layer, and a third magnetic layer are laminated in this order on a non-magnetic support. In the recording medium, the Hc (coercive force) of the ferromagnetic powder in the first RA layer is 500 to 1 sOfloe, and the Hc of the ferromagnetic powder in the third magnetic layer is 800 to 1.1000.
e, and the ferromagnetic powder of the second magnetic layer has an Hc of 500
~800 Oe ferromagnetic powder and Hc 800 ~ 1.10
This magnetic recording medium is characterized in that it is a mixed powder with 0 Oe ferromagnetic powder.

The present invention will be explained in detail below.

One-Layer Structure - The magnetic recording medium of the present invention, as shown in FIG. 3 magnetic layers 3 are laminated in this order.

In the present invention, it is important that the boundaries between the first magnetic layer 1 and the second magnetic layer 2 and the boundaries between the second magnetic layer 2 and the third magnetic layer 3 are clear and flat. .

In addition, in the present invention, for example, an adhesive layer (adhesive layer is also included in this concept) can be provided between the t31 magnetic layer and the non-magnetic support, and a layer opposite to the magnetic layer side of the non-magnetic support can be provided. A back coat layer can be provided on the side surface (back surface).

-Ferromagnetic powder- Each magnetic layer is basically formed by dispersing ferromagnetic powder in a binder resin.

In the present invention, H of the ferromagnetic powder contained in each magnetic layer is
c is important.

That is, the ferromagnetic powder contained in the first magnetic layer has an Hc of 5
The ferromagnetic powder contained in the third magnetic layer has an Hc of 800 to 1.100 Oe, and the ferromagnetic powder of the second magnetic layer has an Hc of 5
00 to 800 Oe and Hc of 800 to 1.
It is a mixed powder with ferromagnetic powder of 100 Oe.

If all of these conditions are satisfied, it is possible to provide a magnetic recording medium that has flat and high electromagnetic conversion characteristics from low to high frequencies.

On the other hand, for example, in the first magnetic layer, H of ferromagnetic powder
If Hc is less than 500 Oe, the electromagnetic conversion characteristics in the mid to high range will deteriorate, and if Hc exceeds 800 Oe,
This is not preferable because the electromagnetic conversion characteristics in the mid to low range deteriorate.

In addition, the Hc of the ferromagnetic powder in the third magnetic layer is 800 Oe.
If Hc is less than 1,100 Oe, the electromagnetic conversion characteristics in the middle to high range will deteriorate, and if Hc exceeds 1,100 Oe, the electromagnetic conversion characteristics in the middle to low range will deteriorate, which is not preferable.

Furthermore, as the ferromagnetic powder of the second magnetic layer, Hc is 500~
800 Oe of ferromagnetic powder and Hc of 800 to 1.1 (1
(If mixed powder with ferromagnetic powder which is loe is not used, 3
In other words, if a mixed powder outside these numerical ranges is used, or a single ferromagnetic powder is used, the continuity of magnetic recording characteristics will be impaired, resulting in deterioration of electromagnetic conversion characteristics, noise, This is undesirable as it leads to an increase in

Therefore, when manufacturing the magnetic recording medium of the present invention, it is recommended to use a mixture of the magnetic paint for the first magnetic layer and the magnetic paint for the third magnetic layer as the magnetic paint for the ft52 magnetic layer.
It's frightening.

In that case, the ratio of the ferromagnetic powder in the first magnetic layer to the ferromagnetic powder in the third fa layer in the above mixture is usually 1 weight to 2.
:8~8.2, tI7 or 4.6~6:4
A particularly preferred ratio is 5:5.

If this riEfil ratio is less than 2/8, the electromagnetic conversion characteristics in the mid to low range may deteriorate;
Exceeding this is not preferable because the electromagnetic conversion characteristics in the mid to high range deteriorate.

In particular, in order to obtain flat characteristics from the low range to the high range, it is desirable that the above weight ratio be 55.

In the present invention, the ferromagnetic powder can be appropriately selected from the following and used as long as the above conditions are satisfied.

For example, Co-containing y-Fe, 0. Powder, Co-containing Fe
,O.

Powder, Co-containing Fed, (4/3 < X < 3
/2) Powder or Fe-A metal powder, Fe-N
i metal powder, Fe-Al-Ni metal powder, Fe-A4
-P metal powder, Fe-)li-3i-A metal powder,
Fe-Ni-3i-^J2-Mn all 2-terminal, Ni-Co
Metal powder, Fe-Mn-Zn metal powder, Fe-Ni
-Zn metal powder, Fe-Co-1-C "metal powder, F
Examples include fine ferromagnetic metal powders such as e-Co-N1-P metal powder, Co-Ni metal powder, and Go-P metal powder.

These ferromagnetic powders can be used alone or in combination of two or more.

Among these, preferred is fine CO-containing -Fe
20 yu powder.

Such ferromagnetic powder has a large Tatewa magnetization and Hc, and is excellent in high-density recording.

In addition, it has a large specific surface area (for example, B E T (1 te 4
By using ferromagnetic powder (0 m''/g or more), it is possible to easily realize a medium that allows high-density recording and has an excellent S/N ratio.

Binder Resin - In the present invention, it is preferable to use a resin modified by introducing a functional group, particularly a modified vinyl chloride resin, a modified polyurethane resin, or a modified polyester resin, as the binder resin contained in each magnetic layer.

Examples of the functional group include -3OsM, -0SO
*M, -COOM and OM' / Su (The tatami formula ΦM is a hydrogen atom or an alkali metal such as lithium or sodium. Ml and Ml are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group. It is preferable that Ml and A2 may be the same or different.

If the modified resin contains such a functional group, the compatibility between the modified resin and the ferromagnetic powder will be improved, and the dispersibility of the ferromagnetic powder will be further improved. The stability of the working fluid is further improved, the frequency characteristics from high to low frequencies are improved in a well-balanced manner, and the durability of the magnetic recording medium is improved in addition to the electromagnetic conversion characteristics.

The modified resins can be used alone or in combination of two or more.

The modified resin includes a vinyl chloride resin, a polyurethane resin, or a polyester resin, and a compound having a negative functional group and chlorine in the molecule, such as 6-CIl, CH, S.
O,M, C-C112CII□O3O,M.

C Emperor-CIl, C00M, ON'嘗6文-CI+' -P-0 Old・ (Tatashi, M, M', M" are the same as above,
do. ) can be produced by condensation with compounds such as by dehydrochloric acid reaction.

Note that in the present invention, thermoplastic resins and thermosetting resins conventionally known in the field of magnetic recording media are used.

A reactive resin, an electron beam curable resin, or a mixture thereof can be used, or they can be used in combination with the modified resin.

Examples of the thermoplastic resin include heavy vinyl M,
Acrylic acid vinyl copolymer, vinyl chloride-vinylidene chloride chloride polymer, chloride and vinylidene-acrylonitrile copolymer, acrylic acid ester-axolonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-chloride Vinylidene copolymer, methacrylic M ester-ethylene copolymer, polyvinyl fluoride,! ! Vinylidene I-acrylonitrile copolymer, acrylonitrile-butadiene Rff<combination, polyamide 41111, polyvinyl butyral, cellulose derivative (cellulose acedate tstylate), cellulose diacetate, cellulose tosoacetate, cellulose propionate, nitrocellulose, etc.), Examples include styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer 2-amino S+ resin, and synthetic rubber-based thermoplastic resin.

These may be used alone or in combination of two or more.

As the thermosetting resin or reactive resin.

For example, phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, methacrylate copolymers and diisocyanate prepolymers. Examples include mixtures with polymers, urea formaldehyde resin 2 and polyamine resins.

These may be used alone or in combination of two or more.

Examples of the electron beam curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type; , urethane acrylic type, epoxy acrylic type, phosphate ester acrylic type, aryl type, and hydrocarbon type.

These may be used alone, or 21! The above may be used in combination.

The binder resin composition in the magnetic layer is usually 1 to 200 parts by weight per 100 parts by weight of the ferromagnetic powder.
Preferably it is 1 to 50 parts by weight.

If the amount of binder resin blended is too high, the amount of ferromagnetic powder blended will be reduced, which may reduce the recording density of the magnetic recording medium, and if the blended amount is too small, the strength of the magnetic layer will decrease. However, the running durability of the magnetic recording medium may decrease.

In the present invention, an aromatic or aliphatic polyisocyanate can be used in combination with the binder resin as a curing agent.

Examples of aromatic polyisocyanates include tolylene diisocyanate (TD I ) and adducts of this with active hydrogen compounds, and have an average molecular weight of 100 to 30.
A value in the range of 00 is preferred.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMDI) and adducts of this with active hydrogen compounds, and have an average molecular weight of 10
Those in the range of 0 to 3000 are preferred, and non-alicyclic polyisocyanates and adducts of these with active hydrogen compounds are more preferred.

The amount of the aromatic or aliphatic polyisocyanate added is usually 1/20 to 1/20 by weight relative to the binder resin.
7/10. Preferably it is 1710 to 1/2.

-Other Components- In the magnetic recording medium of the present invention, the magnetic layer may contain various additive components such as a lubricant, non-magnetic abrasive particles, conductive powder, and surfactant, if necessary. .

Examples of the lubricant include silicone oil, graphite, molybdenum disulfide, and
About 0 monobasic fatty acids (for example.

Examples include fatty acid esters consisting of stearin (stearin) and a monohydric alcohol having about 3 to 26 carbon atoms.

Examples of the non-magnetic abrasive particles include alumina [
α-AIl10! (corundum, etc.)], artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (jE components: corundum and magnetite), etc. The content of this abrasive particle is 20 f per 1 ferromagnetic powder!
! The average particle size is preferably 0.5 #Lm or less (more preferably 0.4 #Lm or less).

Incidentally, when the lubricant and non-magnetic abrasive particles are particularly contained in the outermost magnetic layer, the contact characteristics with the head (sliding performance, wear resistance, etc.) can be significantly improved.

Examples of the conductive powder include carbon black, graphite, silver powder, and nickel powder.

The average particle size of these conductive powders is usually between 10 and 500 m.
A range of pots is preferred.

Examples of the surfactant include natural, nonionic, anionic, and cationic mono-ampholytic surfactants.

By incorporating these conductive powders and surfactants into the magnetic layer, especially the outermost layer, it is possible to effectively lower the surface electrical resistance, thereby reducing noise generation due to discharge of Ii1 electric charge and dropout due to dust adhesion. It is possible to prevent this.

- Non-magnetic support - Materials for forming the non-magnetic support include, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose derivatives such as cellulose triacetate and cellulose diacetate. ,polyamide,
Plastic such as polycarbonate, Cu, A11.2
Examples include metals such as n, glass, boron nitride, Si carbide, and ceramics.

The form of the non-magnetic support is not particularly limited, and main forms include tape, film, sheet, card, disk, and drum.

There are no particular restrictions on the thickness of the non-magnetic support, but for example, in the case of a film or sheet, it is usually 3 to 100 μm,
Preferably, the thickness is 5 to SO#Lm, approximately 30 gm to 10 mm in the case of a disk or card shape, and appropriately selected depending on the recorder etc. in the case of a drum shape.

Note that this nonmagnetic support may have a single layer structure or a multilayer structure.

Further, this non-magnetic support may be subjected to surface treatment such as corona discharge treatment.

1. Manufacture of magnetic recording medium - The method of manufacturing the magnetic recording medium of the present invention is not particularly limited, and can be manufactured according to a known method of manufacturing a multi-layered magnetic recording medium.

For example, for boat fishing, a magnetic paint is prepared by cross-dispersing magnetic layer-forming components such as ferromagnetic powder and binder resin in a solvent, and then the magnetic paint is applied sequentially or simultaneously to the surface of a non-magnetic support.

Examples of the above solvent include acetone, methyl ethyl ketone (MEN), methyl isotutyl ketone (MIBK).
, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propatool, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester series such as ethylene glycol 1000 acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, ether series such as dioxane: Aromatic hydrocarbons such as benzene, toluene, xylene, methylene chloride, ethylene chloride, carbon tetrachloride chloroform, ethylene It is possible to use halogenated hydrocarbons such as chlorohydrin and dichlorobenzene.

When preparing a magnetic coating material, the above-mentioned ferromagnetic powder and other magnetic layer forming components are charged into a mixer simultaneously or individually.

For example, adding the ferromagnetic powder to a solution containing a dispersant,
After kneading for a predetermined time, the remaining components are added and kneading is continued to form a magnetic paint.

Various types of kneading machines can be used to cross-disperse the components forming the magnetic layer.

Examples of this kneading machine include a two-roll mill, a Miki roll mill, a ball mill, and a pebble mill.

Sight grinder, 3qegvari attritor, high speed impeller dispersion machine, high speed stone mill, high speed impact mill, disper kneader-1 high speed mixer homogenizer, a sonic separator, etc.

Examples of the coating method include a wet-on-wet method and a wet-on-dry method. Among these, the wet-on-wet method is preferred.

The wet-on-wet method has an advantage over other coating methods in that it can significantly shorten the mounting process.

Application methods for magnetic paint include, for example, gravure coating method, knife coating method, wire bar coach ink method, doctor plate coat ink method, reverse roll coating method, dip coating method, air knife coating method, calendar coach ink method, and ski coating method. Examples include the zucchi coating method, the kiss coating method, and the fantin coating method.

After applying a magnetic paint to the surface of a non-magnetic support, the undried paint film is generally subjected to a magnetic field orientation treatment, and then a surface smoothing treatment is performed using a super calender roll, etc. You can get it.

FIG. 1 shows the above-mentioned process. The non-magnetic support 5 unwound from the roll 4 is coated with magnetic paint by the coating device 6, and is then coated with the magnetic paint in the first stage magnetic field orientation device M7 and the second stage magnetic field orientation device 8 (
After being dried in the drying device 9, the material is subjected to surface smoothing treatment in the supercalender device 10, and then wound onto a roll 11.

A magnetic recording medium can be obtained by cutting the raw material thus obtained into desired shapes and dimensions.

[Example 1] Next, examples and comparative examples will be listed.
will be explained more specifically.

In addition, in the following, "part" represents "part by weight".

(Examples 1 to 6, Comparative Examples 1 and 2) Each of the 1ii compositions shown in Table 1 was kneaded and separated.
While preparing the magnetic paint and the third magnetic paint, the first
A second magnetic paint was prepared by mixing the magnetic paint and the ll's3 magnetic paint so that the weight ratio of the ferromagnetic powder was as shown in Table 3.

Next, each magnetic paint was applied on a polyethylene terephthalate base (film form) with a thickness of 14 μm according to the process shown in Figure 1 so that the thickness of each layer after drying or the film thickness shown in Table 3 was obtained, and the magnetic paint was oriented in a magnetic field. Treatment, drying treatment, and supercalender treatment were sequentially performed.

Subsequently, a paint having the composition shown in Table 2 was applied to the back side of the polyethylene terephthalate base and dried to a thickness of I.
A non-ink coating layer of #Lm was formed.

The obtained original film was cut into 1/2 inch width to produce a videotape.

The performance of this videotape was measured according to the following procedure.

The results are shown in Table 3.

(a) RF specific output Lumy S/N, chroma output, chroma
AM-S/N Color Video Noise Meter (Shihasoku 925D/1)
Detsuki (Japan Victor HR-S 7000
) is expressed as M (dB) with respect to the reference tape.

The frequency of each signal is as follows.

RF specific output 6MHz Lumi S/N 6MHz chroma output 629k Hz chroma-AM-3/N
Using a 629 kHz (b) linear audio output deck (11 pieces HR-S71100 manufactured by Victor Corporation), the values were expressed as values (dB) relative to a reference tape.

Output signal frequency is 500 Hz, 1kHz, 5kHz
, IOkHz.

(Hereinafter, blank spaces) Table 1 [Effects of the Invention] According to the present invention, it is possible to provide a magnetic recording medium with reduced noise and flat and high electromagnetic conversion characteristics from low to high frequencies.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the magnetic recording medium of the present invention, and FIG.
The figure is a process diagram showing a typical manufacturing process for obtaining the magnetic recording medium of the present invention. S...Nonmagnetic support, l...First magnetic layer. 2... Second magnetic layer, 3... Third magnetic layer, 4... Roll, 5... Non-magnetic support, 6... Coating device, 7...
...Pre-stage magnetic field orientation device, 8...Rear stage magnetic field orientation device, 9
...Drying device, lO...Super calender device,
11...Roll. Figure 1 Figure 2

Claims (3)

[Claims] (1) A first magnetic layer, a second magnetic layer and a third magnetic layer are placed on a non-magnetic support.
In a magnetic recording medium in which magnetic layers are laminated in this order, Hc (coercive force) of the ferromagnetic powder of the first magnetic layer is 500 to 500.
800 Oe, and the Hc of the ferromagnetic powder of the third magnetic layer is 80
0 to 1,100 Oe, and the ferromagnetic powder of the second magnetic layer has a Hc of 500 to 800 Oe and a Hc of 8
1. A magnetic recording medium characterized in that it is a mixed powder with ferromagnetic powder of 00 to 1,100 Oe. (2) The magnetic recording medium according to claim 1, wherein the magnetic paint of the second magnetic layer is a mixture of the magnetic paint of the first magnetic layer and the magnetic paint of the third magnetic layer. (3) The weight ratio of the ferromagnetic powder of the first magnetic layer and the ferromagnetic powder of the third magnetic layer in the mixture is 2:8 to 8:2.
The magnetic recording medium according to claim 2.