JPH0423217A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease drop-outs and to improve reproduced output by forming ferromagnetic powder of Co-gamma-FeOX powder and incorporating Si and Zn into the powder. CONSTITUTION:The Co-gamma-FeOX (where 1.35<=X<=1.40) is used as the ferromagnetic powder to be incorporated into the magnetic layer of this invention and simultaneously, the Si is incorporated at 0.30 to 1.0wt.% and the Zn at 0.5 to 2.5wt.% into the powder. The magnetic recording medium has excellent electromagnetic conversion characteristics in this way and the drop-outs are decreased. Particularly the drop-outs (D/O) of a dubbing system of a high-speed printer (HSP) are decreased. The reproduced output is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium, and more specifically, it has excellent electromagnetic conversion characteristics, reduces dropout, and is particularly useful in high speed printers (HSP). The present invention relates to a magnetic recording medium that reduces dropout (Dlo) after dubbing and improves reproduction output.

[Prior Art and Invention to be Solved] Magnetic recording media such as video tapes and audio tapes generally have a coated magnetic layer.

The magnetic layer is made by dispersing ferromagnetic powder in a binder.

Various attempts have been made to improve the electromagnetic conversion characteristics of such magnetic recording media.

One of the new approaches is the selection of ferromagnetic powder.

Especially Co-y-FeO, powder (Tashi 1.33<X<
1.40) is attracting attention.

When X is 1.33, this ferromagnetic powder becomes FexO<, which is called magnetite magnetic powder, and is more Fe2. *The number is increasing.

Originally, there were questions as to whether this ferromagnetic powder had good magnetic properties, high reproduction output, or other features.

(a) X is smaller than 1.4, Si content is 0.3
Since it is less than 0, the magnetic stability over time is poor.

(b) Since it was dispersed in a resin that does not have a functional group as a binder, the dispersibility was poor.

(c) The specific resistance of the surface of the magnetic layer is high, which degrades dropout.

For this reason, with conventional magnetic recording media, even when high-speed dubbing is performed, it is difficult to record with high sound quality and high image quality.

The present invention has been made in view of the above circumstances.

The purpose of the present invention is to have excellent electromagnetic conversion characteristics and reduce dropouts, especially dropouts after dubbing (Dl) in high speed printers (HSP).
It is an object of the present invention to provide a magnetic recording medium that improves reproduction output by reducing the factor (o).

[Means for Solving the Problems] To achieve the above objects, the present invention provides a magnetic recording medium having a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, Ferromagnetic powder Co-y-Fe
Ox (where 1.35≦X≦1.40) is a powder, and the powder contains 0.30 to 1.0% by weight of Si and 0.5 to 2.5% by weight of Zn. This is a magnetic recording medium characterized by:

The present invention will be explained in detail below.

Single Layer Structure The magnetic recording medium of the present invention basically has one or more magnetic layers laminated on the surface of a nonmagnetic support.

A back coat may be provided on the surface of the non-magnetic support on which the magnetic layer is not provided (back surface) for the purpose of improving running properties of the magnetic recording medium, preventing charging, preventing transfer, etc. Furthermore, an intermediate layer such as an adhesive layer may be provided between the magnetic layer and the nonmagnetic support.

Each of the magnetic layers is made by dispersing at least ferromagnetic powder in a binder resin.

In the present invention, it is desirable that the specific resistance of the surface of the magnetic layer is small, specifically 1xlO' to 5x108Ω/
Preferably, it is sq.

If the resistivity exceeds this upper limit, dropout may occur.

Moreover, if the specific resistance is too small, that is, if it is below the above-mentioned lower limit, the amount of carbon black to be filled must be increased, which is undesirable because the electromagnetic conversion characteristics deteriorate.

1. Ferromagnetic Powder In the present invention, the ferromagnetic powder contained in the magnetic layer is Co-y-FeOx (provided that 1.35≦X≦1.
40) Use of powder, and at the same time Si or 0.3
0-1. Ojl amount% and Zn 0.5-2.5% by weight
It is important that it is contained.

As a result, the magnetic recording medium of the present invention not only has excellent electromagnetic conversion characteristics, but also reduces dropouts, especially dropouts (Dlo) in high-speed printers (H3P), and improves playback output. It can be improved.

X months of the ferromagnetic powder is less than 35, F e 2
The oxidation stability of * is unstable, the stability of magnetic properties over time deteriorates, and when X exceeds 1.40, the saturation magnetization (σ1), which is a magnetic property, decreases and the specific resistance of the magnetic material decreases. This is not desirable as it increases the amount of

Furthermore, if the Si content in the ferromagnetic powder is less than 0.10% by weight, the stability of the magnetic properties of the magnetic material over time will deteriorate;
If the Si content exceeds 0% by weight, the dispersibility of the magnetic material during preparation will deteriorate, making it impossible to obtain a uniform magnetic material, which is not preferable.

Furthermore, if the Zn content in the ferromagnetic powder is 0.5% by weight, it becomes difficult to uniformly add cobalt during preparation of the magnetic material, and if the Zn content exceeds 2.5% by weight, , which is undesirable because it deteriorates the magnetic properties.

In the present invention, to obtain Co-γ-Fed powder with specified Si content and Zn content, a known manufacturing method,
For example, Japanese Patent Publication No. 56-49856 and Special Publication No. 57-
The manufacturing method described in Publication No. 37532 and the like may be followed.

In the present invention, it is important to use the ferromagnetic powder specified above, but it is also possible to use this ferromagnetic powder in combination with conventionally known ferromagnetic powders.

In this case, the ratio of the latter to 100 parts by weight of the former is usually 0.1 to 5 parts by weight.If the ratio of the latter exceeds 5 parts by weight, the effect of the present invention may be reduced. Therefore, it is not desirable.

Conventionally known ferromagnetic powders include, for example, Co-containing y
-Fe, O, powder, Go-containing FeJn powder, or F
e-A metal powder, Fe-Ni metal powder, Fe-A
4-Ni metal powder, Fe-An-P metal powder, Fe-
Ni-3i-A metal powder, Fe-Ni-5i-^l-
Mn metal powder, Xl-C.

Metal powder, Fe-Mn-Zn metal powder, Fe-Ni-Z
n metal powder, Fe-Co-Ni-Cr metal powder, Fe-
Co-N1-P metal powder, Co-Ni metal powder and C
(Fine ferromagnetic metal powder, such as .-P metal powder, etc.).

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

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

The ferromagnetic powder used for the magnetic layer in the present invention generally has a coercive force (Hc) value of 500 to 1,00 Oe, preferably 600 to 900 Oe.

If the above-mentioned coercive force is less than 500 millimeters, the high-frequency video signal output may decrease, and if the coercive force is less than 1,
If it exceeds 000 oersted, it is undesirable because the output of low-frequency color signals will decrease.

Also, what is the specific surface area of the ferromagnetic powder used in the present invention?

When expressed as a BET value, it is usually 20 to 90 m'/g, preferably 25 to 65 m2/g.

When the specific surface area is within this range, it is possible to easily realize a medium that allows high-density recording and has an excellent S/N ratio.

Further, the ferromagnetic powder used in the present invention usually has a major axis length of 0.
10-0.40 am and an axial ratio of 6-14.

If the major axis length is less than 0.1 μm, the dispersibility of the paint may become difficult, and if it exceeds 0.40 gm,
This is not desirable because the particles are large and the noise becomes high.

In addition, if the axial ratio is less than 6, the orientation ratio will decrease and 1
If it exceeds 4, the output will decrease, which is not preferable.

The shape of the ferromagnetic powder used in the present invention is not particularly limited as long as it is fine, and for example, any shape such as acicular, spherical, or ellipsoidal shape can be used.

(1) Binder (1) In the present invention, a resin modified by introducing a functional group, particularly a modified vinyl chloride resin, is used as a binder to be contained in each magnetic layer.
It is preferable to use a modified polyurethane resin (urethane elastomer is also included in this category) or a modified polyester resin.

The functional group is, for example, -So3M-OS02M
, -COOM and OM' / P \ OM'' (In the formula, M is a hydrogen atom or an alkali metal such as lithium or sodium, and Ml and N2 are a hydrogen atom, lithium, potassium, sodium, or an alkyl group, respectively. It is preferable that Ml and N2 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 not only be further improved, but also its agglomeration will be prevented. The stability of the coating liquid is further improved, and as a result, the frequency characteristics from high to low frequencies are improved in a well-balanced manner, and in addition to the electromagnetic conversion characteristics, the durability of the magnetic recording Ij1 medium is also improved.

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

In the latter case, it is preferable to use a modified polyurethane resin and a modified vinyl chloride resin together.

The modified resin is a compound having a vinyl chloride resin, a polyurethane resin, or a polyester resin and a negative functional group and chlorine in the molecule, such as CJl-CHt CH25.
O, III, C1-CH3CN, 03O2111, C
jl CHtCOOM, OM'C-C
It can be produced by condensing a compound such as H"-P~0 by a dehydrochloric acid reaction.

Note that in the present invention, thermoplastic resins and thermosetting resins that are 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.

In the latter case, preferred for the purposes of the present invention is the combined use of the modified resin and vinyl chloride-vinyl acetate copolymer.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-donylidene chloride Copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, Bois vinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral ,
Cellulose derivative (cellulose acetate butyrate)
, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.)
, styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber-based thermoplastic resin.

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

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and isocyanate prepolymer. mixtures of methacrylate copolymers and shiisocyanate prebolimers, urea formaldehyde resins, and polyamine resins.

These may be used alone, or 2! ! The above may be used in combination.

Examples of the electron beam irradiation curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic polyurethane, polyurethane acrylic type, polyamide acrylic type, etc. Examples include polyfunctional monomers such as type, urethane acrylic type, epoxy acrylic type, #I# ester acrylic type, aryl type, and heterocarbon type.

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

The blending amount of the binder in the magnetic layer is as follows:
The amount is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight.

If the amount of binder 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 be reduced. However, the running durability of the magnetic recording medium may be reduced.

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

Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI) and adducts of this with active hydrogen compounds, and have an average molecular weight of 100 to 3.00.
A value in the range of 0 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 1/10 to 1/2.

-Other components- In the magnetic recording medium of the present invention, the magnetic layer may contain, for example, a lubricant, non-magnetic abrasive particles, conductive powder,
Various additive components such as surfactants can be included.

Examples of the above-mentioned lubricants include silicone oil, graphite, molybdenum disulfide, carbon atoms of 12 to 2
About 0 monobasic fatty acids (for example.

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

Examples of the non-magnetic abrasive particles include alumina [
α-AltO! (corundum), etc.], artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (
Main components: corundum and magnetite).

The content of the abrasive particles is preferably 20 parts by weight or less per 1 ferromagnetic powder, and the average particle size is 0.5 parts by weight or less.
gm or less is good, and 0.4 gm or less is even better.

Incidentally, if the lubricant and nonmagnetic abrasive particles are particularly contained in the second 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,
Examples of the surfactant include graphite, silver powder, and nickel powder. Examples of the surfactant include natural, nonionic, anionic, cationic, and amphoteric surfactants.

These conductive powders and surfactants, especially t! By appropriately containing it in the No. 142 magnetic layer, the surface electrical resistance can be effectively lowered, and it is possible to prevent the generation of noise due to the discharge of withstand charges and the occurrence of dropouts due to the adhesion of dust.

In addition, when carbon black is used as the conductive powder, for example, the particle size of the carbon black is 13 to 50p.
It is preferable that it is m.

-Nonmagnetic support- Examples of the material forming the nonmagnetic support include 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,
Plastics such as polycarbonate, Cu, ^l, Z
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, cart, disk, and drum.

Is there any particular restriction on the thickness of the non-magnetic support? For example, in the case of a film or sheet, it is usually 3 to 1100p,
Preferably it is 5 to 50 pm, and in the case of a disk or cart shape, it is about 3D#Lm to 10 mm, and in the case of a drum shape, it is appropriately selected depending on the recorder, etc.

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 method applied to the manufacture of known multilayer structure type magnetic recording media.

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

Examples of the above solvent include acetone, methyl ethyl ketone (IIIEK), methyl isobutyl ketone (ill
BK), Ketones such as cyclohexanone: Alcohols such as methanol, ethanol, and propatool; Esters such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol dinoacetate: cyethylene glycol dimethyl Ethers such as ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; Aromatic hydrocarbons such as benzene, toluene, and xylene; Halogenated materials such as methylene chlorite, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Hydrocarbons and the like can also be used.

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.

To cross-distribute the components forming the magnetic layer, various types of cross-talk machines can be used.

Examples of this mixer include a two-roll mill, a three-roll mill, a ball mill, a pebble mill site grinder, a Sqegvari attritor, a high-speed impeller dispersion machine, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer homogenizer, Examples include ultrasonic dispersion machines.

Examples of application methods include wet-on-wet (
wet-on-wet method, wet-on-dry method, dry-on-wet method, dry-on-try method -dry) method.

Among these, the wet-on-wet method and the wet-on-try method are preferred, and the wet-on-wet method is particularly preferred.

The wet-on-wet method has advantages over other coating methods in that it has excellent productivity and it is easy to thin the upper layer.

Examples of methods for applying magnetic paint include clavia coating method, knife coating method, wire bar coating method, tractor plate coating method, and reverse roll coating method.

Examples include a dip coating method, an air knife coating method, a calendar coach ink method, a squeegee coating method, a kiss coating method, and a fantine coating method.

After applying magnetic paint to the surface of a non-magnetic support, the undried paint film is generally subjected to a magnetic field orientation treatment.
A magnetic recording medium can then be obtained by subjecting the material to a surface smoothing treatment using a super calender roll or the like, and then cutting it into a desired shape.

[Example] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

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

(Examples 1 to 5, Comparative Examples 1 to 3) A magnetic paint was prepared by mixing and dispersing the following paint composition, and the magnetic paint was coated on a polyethylene terephthalate film with a thickness of 15.0 Bm and dried to form a monochrome film with a thickness of 3.5 pm. A magnetic recording medium was manufactured by forming a magnetic layer.

Further, this magnetic recording medium was cut to obtain a 1/2-inch video tape.

Co-y -FeOx powder (X, Si content, Zn content is listed in Table 1, He/BET = 680/
30゜ Long axis length 0.25 gm, axial ratio 10)...Amount listed in Table 1 Co y Fe2O: + powder (Hc/ BET =
680/30 long sleeve long Q4Sgm, axial ratio 10)...
Amounts listed in Table 1 Vinyl chloride resin (listed in Table 1) 10 parts Polyurethane (MIj 43.7g 0°C) 5 parts Polyisocyanate... ...-. 5 parts carbon black (particle size 20mJ4) .....Amount α- listed in Table 1
Sentence A, 03 (0.2 mg) 5 parts myristic acid 0.8 parts stearic acid ...0.8 parts Butyl stearate...1.0 parts Cyclohexanone
...... Appropriate amount of methyl ethyl ketone...
・・・・・・ Appropriate amount of toluene ・・・・・・・・・・・・・・・
・Appropriate amountNext, the electromagnetic conversion characteristics of these videotapes (
RF ratio output, output after transfer by H3P D10, H5P
The Dlo after transfer was measured in the following manner.

The result! $2 Shown in the table.

RF specific output ra video noise meter (Shihasoku r925D/I
(l (dB)
I asked for

Dlo: Using a dropout counter VD-5M (manufactured by Nippon Hector Co., Ltd.) or VHOIAZ (manufactured by Shihasoku), 10
psec or longer, and the output of the RF envelope is 1.
The output that was lower than 4 dB was treated as one trouge out, and the total length was measured, and the average value per minute was calculated.

(Example 6) A coating composition for the first magnetic layer was prepared by mixing and dispersing the coating composition in Example 1, and a coating composition for the second magnetic layer was prepared by mixing and dispersing the following coating composition. did.

110E Co-y-Fe20i powder (Si content 0.4% by weight
Hc/BET = 800/'45. Long axis length 0.2
0gm, axial ratio 10)・・・・・・・・・・・・ 10
0 parts Vinyl chloride resin (contains SO, Na groups) 10 parts polyurethane (MW ls:I, Tg-20°C) 5 parts polyisocyanate・・・・・・ 5 parts carbon black (ti diameter 45 ml) 0.3 parts α-A 01 (0.2 mp) ・・・・・・・・・5 parts myristic acid 0.7 parts stearic acid 0.7 parts butyl stearate ... 0.9 parts cyclohexanone
...... Appropriate amount of methyl ethyl ketone...
・・・・・・ Appropriate amount of toluene ・・・・・・・・・・・・・・・
・Appropriate amount Next, apply 2.5 g of the above two types of paint onto a 15.0 μm thick polyethylene terephthalate film using a wet-on-wet simultaneous multilayer coating method.
A first magnetic layer having a thickness of m and a second magnetic layer having a thickness of 0.5 JLm were formed to produce a magnetic recording medium.

Furthermore, this magnetic recording medium was cut to obtain a 1/2 inch wide video tape.

The physical properties of this videotape were measured in the same manner as in Example 1, and the results are shown in Table 2.

(Example 7) A coating material for the first magnetic layer was prepared by mixing and dispersing the components of the coating composition Ii in Example 3, and a coating material for the second magnetic layer was prepared in the same manner as in Example 6.

A videotape was produced in the same manner as in Example 6 except that the thickness of the second magnetic layer was OJ gm, and its physical properties were measured.

The results are shown in Table 2.

(Hereinafter, blank space) [Effects of the Invention According to the present invention, it has excellent electromagnetic conversion characteristics and reduces dropouts, especially dropouts after dubbing (Dl) in high-speed printers (HSP).
It is possible to provide a magnetic recording medium that improves reproduction output by reducing (o).

Claims (3)

[Claims] (1) In a magnetic recording medium having a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, the ferromagnetic powder is Co-γ-FeO_X (where 1.35≦X≦1
．． 40) It is a powder, and the powder contains Si from 0.30 to
A magnetic recording medium characterized in that it contains 1.0% by weight and 0.5 to 2.5% by weight of Zn. (2) The magnetic recording medium according to claim 1, wherein the binder is a binder containing a negative functional group. (3) The specific resistance of the surface of the magnetic layer is 1×10^7 to 5×
The magnetic recording medium according to claim 1 or 2, which has a resistance of 10^8 Ω/sq.