JPH0467427A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a noise, and to improve S/N, and simultaneously, to manifest the electromagnetic conversion characteristic of a lower layer equally to or more than that of an upper layer by forming an (n-1)-th magnetic layer of the mixed component of an n-th magnetic layer forming component and an (n-2)-th magnetic layer forming component. CONSTITUTION:A magnetic recording medium is constituted by forming a first magnetic layer 1, a second magnetic layer 2,..., an (n-2)-th magnetic layer (n-2), and an (n-1)-th magnetic layer (n-1), and an n-th magnetic layer (n) (n>=3 is integer larger) in this order on a non-supporting body B. Then, the (n-1)-th magnetic layer (n-1) is formed of the mixed component of the N-th magnetic layer forming component and the (n-2)-th magnetic layer (n-2) forming component. Thus, the occurrence of the noise can be prevented, and S/N can be improved, and simultaneously, the electromagnetic conversion characteristic of the lower layer can be manifested equally to or more than that of the upper layer.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a magnetic recording medium and a method for manufacturing the same, and more specifically, in a magnetic recording medium having a multilayered magnetic layer, it is possible to prevent noise generation and improve S/ The present invention relates to a magnetic recording medium that can improve N and exhibit electromagnetic conversion characteristics of a lower layer equal to or better than those of an upper layer, and a manufacturing method that can efficiently manufacture the same.

[Prior art and inventions? Question 8] In recent years, in order to improve various characteristics, magnetic recording media having a multilayer magnetic layer instead of a single layer magnetic layer have appeared.

However, it is known that in this type of magnetic recording medium, noise is likely to occur due to the influence of the boundary between the upper layer and the lower layer, resulting in a deterioration of the S/N ratio.

As a countermeasure for this, has a technology been developed to create a mixing region between the upper layer and the lower layer where the components change continuously (Japanese Unexamined Patent Publication No. 53-241721)? This technology can prevent S/N deterioration, etc. Even if it is possible to do so, the problem is that the electromagnetic conversion characteristics of the underlying layer will not improve.

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

That is, an object of the present invention is to prevent the generation of noise and improve the S/N in a magnetic recording medium having a multilayered magnetic layer, and to develop the electromagnetic conversion characteristics of the lower layer to be as good as or better than that of the upper layer. An object of the present invention is to provide a magnetic recording medium that can be used as a magnetic recording medium, and a method for manufacturing the same.

[Means for Solving the Problems] The magnetic recording medium of the present invention for achieving the above objects comprises a first magnetic layer, a second magnetic layer,... an nth magnetic layer (n is an integer of 3 or more) in this order, the (n-1)th magnetic layer is composed of a mixed component of an n-th magnetic layer-forming component and a (n-2)-th magnetic layer-forming component. This is a magnetic recording medium characterized by:

The manufacturing method of the present invention also provides a magnetic recording medium in which a first magnetic layer, a second magnetic layer, ... an nth magnetic layer (n is an integer of 3 or more) are provided in this order on a nonmagnetic support. In the manufacturing method, a mixed paint of a magnetic paint for the n-th magnetic layer and a magnetic paint for the 8 (n2) magnetic layer is applied on the undried (n-2) magnetic layer to form the (n = 1) magnetic layer. This is a method for manufacturing a magnetic recording medium, characterized in that a layer is formed, and then an n-th magnetic layer is formed thereon while the core layer is not dried.

The present invention will be explained in detail below.

The magnetic recording medium of the present invention basically has a structure in which three or more magnetic layers are laminated on a non-supporting body.

That is, as shown schematically in No. 11J, the non-supported body B
A first magnetic layer l, a second magnetic layer 2, ... (n-2)th magnetic layer are formed on the top.
It has a structure in which a magnetic layer (n-2), a (n-1)th magnetic layer (n-1) magnetic layer, and an nth magnetic layer n (n is an integer of 3 or more) are provided at this j@.

Each magnetic layer is basically made by dispersing ferromagnetic powder in binder resin.

Note that an adhesive layer (
An intermediate layer such as an adhesive layer (also included in this concept) can be provided, and a back coat layer can be provided on the surface of the nonmagnetic support opposite to each magnetic layer.

In the present invention, in the above structure, the (n-1)th magnetic layer (n-1) (hereinafter sometimes referred to as a mixed layer) is combined with the n-th magnetic layer forming component and the (n-2)th magnetic layer (n-1) (hereinafter sometimes referred to as a mixed layer). n-2) It is important to form a mixed component with the forming component.

For example, taking a three-layer magnetic layer as an example, the second layer is
It is important that the layer be formed using a mixed component of the first layer forming component and the third layer forming component.

By adopting such a configuration, the magnetic recording medium can
It is possible to prevent the generation of noise and improve the S/N ratio, and to develop the electromagnetic conversion characteristics of the lower layer to be equal to or higher than those of the upper layer.

On the other hand, if the above mixed layer is not provided,
Electromagnetic conversion characteristics, especially Lumi-3/N and Chroma-AM, deteriorate.

In order to manufacture the magnetic recording medium of the present invention, after forming the (n-2)th magnetic layer, while the core layer is still in an undried state, the magnetic properties of the nth magnetic layer are prepared in advance. The mixed paint of the paint and the magnetic paint of the (n-2)th magnetic layer is mixed with the paint of the (n-2)th magnetic layer.
n-2) After coating on the magnetic layer and thus forming the (n-1)th magnetic layer, the n-th magnetic layer is further coated while still wet.
A magnetic layer of magnetic paint is applied thereon.

By this method, it is possible to efficiently manufacture the magnetic recording medium of the present invention.

The above mixed paint, that is, the magnetic paint for the (n-1)th magnetic layer contains the ferromagnetic powder for the n-th magnetic layer and the (n-2)th magnetic powder as ferromagnetic powder.
) and ferromagnetic powder of the magnetic layer, and the weight ratio thereof is preferably 1:4 to 1:0.25.

If the weight ratio is out of the range, the effect of providing the mixed layer will be weakened, and in particular, the S/N ratio may deteriorate.

In the present invention, although the thickness of each magnetic layer is not particularly limited, there are certain preferable conditions for the (n-1)th magnetic layer.

That is, it is preferable that the thickness is less than lpm.

The reason for this is that if the thickness exceeds lpm, it becomes difficult to effectively improve the electromagnetic conversion characteristics of the underlying layer.

Further, the details of the manufacturing method of the magnetic layer forming component 5, the non-magnetic support, and the magnetic recording medium will be described below.

Examples of the ferromagnetic powder contained in the single magnetic layer include Co-containing 7 Fe2O:+ powder, COO-containing FezO4 powder,
Fed with COO, (4/3 < x < 3/2)
powder, or Fe-An metal powder, Fe-Ni metal powder, Fe-A1-Ni metal powder, Fe-Ai-P metal powder, Fe-Ni-5i-A metal powder, FeFe-Ni
-3i-AJI-metal powder, N1-Go metal powder, Fe
Jn-Zn metal powder, Fe-Ni-Zn metal powder, F
e-Go-Ni-Cr metal powder, Fe-Go-Ni-P
Fine ferromagnetic metal powders such as metal powders, Go-Ni metal powders and Go-P metal powders can be mentioned.

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

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

Such ferromagnetic powder has large saturation magnetization and coercive force Hc, and is excellent in high-density recording.

Also, the specific surface area is large (for example, the bet value is 40127
If a ferromagnetic powder is used, it is possible to easily realize a medium that enables 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.

Examples of the functional group include -8O:1M, -0SO
□M, -COOM and OM' (In the formula, M is a hydrogen atom or an alkali metal such as lithium or sodium, and Ml and N2 are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group. , Ml and N2 may be the same or different, etc.) are preferable.

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, but its agglomeration will also be prevented. The stability of the coating liquid 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 resin is 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 -CH2CH2SO,
M, 0 sentences-CH2CH20SO, 11, C2-[
:H2C0O1lI, 0"C or -CH2-
It can be produced by condensing a compound such as P=0 N2 (M, M', N2 have the same meanings as above) through a dehydrochloric acid reaction.

Note that in the present invention, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins conventionally known in the field of magnetic recording media can be used, or these can be used as the modified resin. It can also be used in conjunction with

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl 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.

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.

Examples of the electron beam curable resin include unsaturated prepolymer 2ether acrylic types such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, and polyamide acrylic type. , urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and hydrocarbon type.

In the present invention, one type of binder resin may be used alone, or two or more types may be used in combination.

The blending amount of the binder resin 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 decrease, resulting in a decrease in the recording density of the magnetic recording medium.If the amount blended is too small, the strength of the magnetic layer will decrease. However, the running durability of the magnetic recording medium may be reduced.

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 (TDI) and adducts of this with active hydrogen compounds, and have an average molecular weight of 100 to 3000.
Preferably within the range of .

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 30 0 are preferable, and non-alicyclic polyisocyanates and adducts thereof with active hydrogen compounds are more preferable.

The amount of the aromatic or aliphatic polyisocyanate added is usually 1/20 to 1/20 by weight relative to the binder resin.
7/1O1 is preferably 1/1O 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, surfactant, etc., if necessary.

Examples of the lubricant include silicone oil, graphite, molybdenum disulfide, and
Examples include fatty acid esters consisting of about 0 monobasic fatty acid (for example, stearic acid) and a monohydric alcohol having about 3 to 26 carbon atoms.

Examples of the non-magnetic abrasive particles include alumina [
α-Ai20z (corundum) etc.], artificial corundum,
Examples include fused alumina, silicon carbide, chromium oxide, diamond, synthetic diamond, garnet, and emery (mainly 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 ALm.
Is it less than <, (14 μm or less is even better).

Note that the lubricant and nonmagnetic abrasive particles are particularly
When included in the magnetic layer of the layer, contact characteristics with the head (sliding performance, wear resistance, etc.) can be significantly improved.

Examples of the conductive powder include carbon fluff, graphite, silver powder, and nickel powder, and examples of the surfactant include natural, nonionic, anionic, and
Examples include cationic and amphoteric surfactants.

By incorporating these conductive powders and surfactants into the magnetic layer, especially the top layer, it is possible to effectively lower the surface electrical resistance, thereby preventing the generation of noise due to the discharge of electrical charges and the occurrence of dropouts due to the adhesion of dust. It can be prevented.

Non-magnetic support - Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamide,
Plastics such as polycarbonate, Cu, All, 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.

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 lm,
Preferably, it is 5 to 50 μm, and in the case of a disk or cart shape, it is approximately IO, Bm 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 a surface treatment such as corona discharge treatment.Manufacturing of a magnetic recording medium - There is no particular restriction on the manufacturing method of the magnetic recording medium of the present invention. It can be manufactured according to a known method for 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 solvent include acetone, methyl ethyl ketone (IE), methyl isobutyl ketone (MIBK)
, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propatool, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester systems such as ethylene glycol monoacetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, ether systems such as dioxane, etc. Aromatic hydrocarbons such as benzene, toluene, xylene, etc.: methylene chlorite, ethylene chloride carbon tetrachloride chloroform, ethylene chloride Halogenated hydrocarbons such as hydrin and dichlorobenzene can also be used.

When preparing a magnetic paint, the components for forming the magnetic layer are charged simultaneously or individually into a mixer.

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 crosstalk machines can be used for crosstalk dispersion of the components forming the magnetic layer.

Examples of this cross-mixing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sight grinder, an SQegvari attritor, a high-speed impeller splitter, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer homogenizer, Examples include ultrasonic dispersion machines.

Application methods include, for example, a wet-on-wet method, a wet-on-dry method, and a dry-on-wet method. et)
method, try-on-dry
Methods can be mentioned.

Among these, wet-on-unicorn, wet-on-try, and wet-on-try methods are preferred, with wet-on-try methods being particularly preferred.
On-wet method is preferred.

The wet-on-wet method has advantages over other coating methods in that the adhesive force between the upper and lower layers is stronger and the surface of the magnetic layer is smoother.

Application methods for magnetic paint include, for example, gravure coating, knife coating, wire coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, and squeegee coating. coating method, kiss coating method, and fantine coating method.

After a magnetic paint is applied 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., to achieve the desired shape. A magnetic recording medium can be obtained by cutting it into dimensions and shapes.

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

Note that in the following, "parts" represent "parts by weight."

(Examples 1 to 11, Comparative Examples 1 to 4), L calendar month] U branch] Ferromagnetic powder 100 parts (Co
-y -Fe2O:+, BET value 55m''/g
) Vinyl chloride copolymer...13 parts (contains epoxy group and sulfonic acid metal base) Polyurethane...
......8 parts (aromatic polyester) Stearic acid...2 parts Butyl stearate...2 parts Carbon black・・・
...3 parts (average particle size 40 lm) Alumina dispersion alumina (0.24 m spherical) ...6 parts Polyurethane (aromatic polyester) ... ... 1 part methyl ethyl ketone - toluene cyclohexanone 1:1:1 mixture ... 7 parts Among the components constituting the above upper layer composition, each component except the alumina dispersion, After first mixing 14 parts of methyl ethyl ketone and 14 parts of toluene, the above alumina dispersion was added, and then 40 parts of methyl ethyl ketone and 40 parts of toluene were mixed.
1 part and 60 parts of cyclohexanone were added thereto, thoroughly mixed, and passed through a filter to obtain magnetic paint A.

100 parts (Co
7- Fe2O3, BET value 40m”/g
) Alumina (particle size 0.14m spherical) 5M vinyl chloride copolymer 17 parts (MRIIO manufactured by Nippon Zeon) Polyurethane (contains sulfonic acid metal base)・・・
...13 parts Stearic acid ...1 part Butyl stearate ...1 part Carbon black
...3 parts (particle size 20ILm) After first mixing each component constituting the above lower layer composition with 12 parts of methyl ethyl ketone and 12 parts of toluene, 88 parts of methyl ethyl ketone, 88 parts of toluene, and cyclohexanone were mixed. After mixing thoroughly, 8 parts of trifunctional isocyanate was added and passed through a filter to obtain magnetic paint C.

On the other hand, magnetic paints A and C before being passed through a filter were kneaded and passed through a filter to obtain magnetic paint B for a mixed layer.

Next, using a precision extrusion coater (FEC), the above magnetic paints A, B, and C are coated on a 13 pm thick polyester base (film form) to form an upper layer, a mixed layer, and a lower layer, each with the film thickness shown in Table 1. They were applied at the same time.

Next, before the paint film dries, apply 2000 ml to the solenoid.
After magnetic field orientation at 0 e and further calender treatment, a paint consisting of the following back coat composition was applied to the back side of the polyester base to a film thickness of 0.6 # after drying.
A raw fabric was obtained by applying the coating in an amount of Lm.

This original tape was then cut into a 172 inch width to obtain a sample tape.

Back coat carbon black (particle size 22m a )...100 parts Carbon black (particle size 75mJL)...10 parts Calcium carbonate powder (particle size x: +omuL) 10 parts Nitrocellulose...・40 parts (Asahi Kasei Co., Ltd. Seltsuba BTI (1/2) polyurethane resin...
・・・・・・50 parts (N314 manufactured by Nippon Polyurethane Co., Ltd.)
1 low molecular weight type MW 50,000, hydroxyl group, urethane main chain contains secondary amine and tertiary amine) Polyisocyanate compound...15 parts (Coronate 3041) Cyclohexane... 275 parts methyl ethyl ketone 500 parts toluene
500 copies Next, the electromagnetic conversion characteristics of the sample tape were measured in the following manner.

The results are shown in Table 1.

Further, FIG. 2 shows the relationship between the proportion of ferromagnetic powder in the mixed layer and the electromagnetic conversion characteristics, and FIG. 3 shows the relationship between the film thickness of the mixed layer and the electromagnetic conversion characteristics.

(a) RF ratio output The output during reproduction of a 00% white signal is determined in comparison with the tape of Comparative Example 1 (reference tape).

(b) Using the Lumi S/N noise meter (manufactured by Shihasota), use the reference tape [
[manufactured by Konica Corporation], the difference in S/N of the sample tape at 100% white signal is determined.

(c) Chroma output The output of the chroma signal during playback was compared to the tape of Comparative Example 1 (
Determined by comparison with standard tape).

(d) Chroma-AM Use a noise meter (manufactured by Shihasoku).

In comparison with a reference tape [manufactured by Konica Corporation], the difference in S/N of the sample tape in chroma signals is determined.

(Hereinafter, blank space) [Effects of the Invention] According to the present invention, it is possible to prevent the generation of noise, improve the S/N ratio, and develop the '$L magnetic conversion characteristics of the lower layer to be equal to or higher than that of the upper layer. It is also possible to provide a magnetic recording medium with a multilayer structure.

Further, according to the present invention, it is possible to provide a manufacturing method that can efficiently produce the above magnetic recording medium.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of the magnetic recording medium of the present invention. FIG. 2 shows the relationship between the proportion of ferromagnetic powder in the mixed layer and the electromagnetic conversion characteristics, and FIG. 3 shows the relationship between the thickness of the mixed layer and the electromagnetic conversion characteristics. B...Nonmagnetic support, 1...First magnetic layer, 2...
Second magnetic layer, (n-2)... (n-2)th magnetic layer, (
n-1)...(n-1)th magnetic layer, n...nth magnetic layer. 8. Contents of Supplement 1 ■ August 1990, 10il Meihi-sen, page 1, line 3

Claims (1)

[Claims] (1) A first magnetic layer, a second magnetic layer, etc. on a nonmagnetic support.
- In a magnetic recording medium in which the nth magnetic layer (n is an integer of 3 or more) is provided in this order, the (n-1)th magnetic layer includes the nth magnetic layer forming component and the (n-2)th magnetic layer forming component. A magnetic recording medium characterized by comprising a mixed component of. (2) Claim 1, wherein the (n-1)th magnetic layer has a thickness of 1 μm or less.
The magnetic recording medium described in . (3) The (n-1)th magnetic layer has a weight ratio of ferromagnetic powder of the n-th magnetic layer to ferromagnetic powder of the (n-2)th magnetic layer of 1:4.
The magnetic recording medium according to claim 1 or 2, containing a mixed powder having a ratio of ~1:0.25. (4) A first magnetic layer, a second magnetic layer, etc. on a nonmagnetic support.
- In a method for manufacturing a magnetic recording medium in which an n-th magnetic layer (n is an integer of 3 or more) is provided in this order, an undried (n-th magnetic layer)
2) Magnetic paint for the nth magnetic layer and the (n-2)th magnetic layer on the magnetic layer.
Applying a mixed paint with the magnetic paint for the magnetic layer, the (n-1)
1. A method of manufacturing a magnetic recording medium, comprising forming a magnetic layer, and then forming an n-th magnetic layer thereon while the layer is not dry.