JPH0461622A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent wind-tightening as well as whitening and sliding noise by specifying the weight ratio of a hardening agent to a binder in the uppermost layer to the equal or less to the weight ratio of a hardening agent to a binder in a magnetic layer except for the uppermost layer. CONSTITUTION:The magnetic recording medium has a magnetic layer comprising a first magnetic layer 1 and a second magnetic layer 2 formed on a nonmagnetic supporting body S. The weight ratio of a hardening agent to a binder in the uppermost layer 2 is made equal or less to the weight ratio of a hardening agent to a binder in a magnetic layer 1 except for the uppermost layer. If the weight ratio of the hardening agent to the binder in the uppermost layer 2 exceeds that of the hardening agent to the binder in the magnetic layer 2 exceeds that of the hardening agent to the binder in the magnetic layer except for the uppermost layer, all of whitening, sliding noise and wind-tightening can not be prevented at one time. Thereby, wind-tightening as well as whitening and sliding noise can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium that effectively prevents the occurrence of clouding and sliding noise, and also prevents tight winding.

[Prior Art and Problems to be Solved by the Invention] In order to improve the characteristics of magnetic recording media such as video tapes and audio tapes, a plurality of magnetic layers have been conventionally formed on a non-magnetic support.
It is known to form one magnetic layer and add a hardening agent to the magnetic layer.

However, it is difficult to control the amount of curing agent blended, and various inconveniences occur depending on whether it is too much or too little.

For example, in a magnetic recording medium consisting of an upper layer and a lower magnetic layer, if the amount of curing agent in the upper layer is too large, the surface of the upper layer will become hard, resulting in poor head contact and frequent clouding and sliding noise. .

Furthermore, if the amount of the curing agent in the lower layer is less than that in the upper layer, the curing will tend to be tightly wound and wrinkles will easily occur on the surface of the upper layer.

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

That is, an object of the present invention is to provide a magnetic recording medium in which a curing agent is blended into a plurality of magnetic layers, which effectively prevents clouding, sliding noise, and winding tightness.

[Means for Solving the Problems] To achieve the above objects, the present invention provides a magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, in which a hardening agent for a binder contained in the uppermost layer is used. The magnetic recording medium is characterized in that the weight ratio of the curing agent to the binder contained in the magnetic layers other than the top layer is equal to or less than the weight ratio of the hardening agent to the binder contained in the magnetic layers other than the uppermost layer.

The present invention will be explained in detail below.

Single Layer Structure The magnetic recording medium of the present invention has a plurality of magnetic layers laminated on a nonmagnetic support.

As a specific example of a magnetic recording medium, a first magnetic layer 1 and a second magnetic layer are formed on a non-magnetic support S as shown in FIG.
A magnetic recording medium formed by stacking magnetic layers consisting of a magnetic layer (top layer) 2, a non-magnetic support S as shown in FIG.
A magnetic recording medium may be mentioned in which a magnetic layer consisting of a first magnetic layer 1, a second magnetic layer 2, and a third magnetic layer (top layer) 3 is laminated thereon.

Note that in the present invention, an adhesive layer (adhesive layer is also included in this concept) can be provided between the non-magnetic support and the magnetic layer, and an adhesive layer can be provided on the opposite side of the non-magnetic support from the magnetic layer. A back coat layer may be provided on the surface (back surface).

One Magnetic Layer - The magnetic layer basically contains ferromagnetic powder, a binder, and a hardening agent.

In the present invention, the weight ratio of the curing agent to the binder contained in the uppermost layer of the magnetic layer is equal to or less than the weight ratio of the curing agent to the binder contained in the magnetic layers other than the two-most magnetic layer. ,is important.

By satisfying this condition, the magnetic recording medium can effectively prevent cloudiness, sliding noise, and winding tightness.

On the other hand, if the weight ratio of the hardening agent to the binder contained in the top layer exceeds the weight ratio of the hardening agent to the binder contained in the magnetic layers other than the top layer, all of the above effects cannot be achieved at the same time. .

The weight ratio of the curing agent to the binder contained in the outermost layer is preferably 50% by weight or less.

The reason for this is that if this weight ratio exceeds 50% by weight, head cloudiness and sliding noise may become worse, and winding may become tight during curing, which is undesirable.

Examples of the ferromagnetic powder suitably used in the present invention include Co-containing y-Fe2O powder, Co-containing Fe=0° powder, Goo Fed, (4/3 < x < 3/2
) powder, or Fe-An metal powder, Fe-Ni metal powder, Fe-AJLNi metal powder, Fe-AM-P metal powder, Fe-Nj-3i-AfL metal powder, Fe-
NFe-Ni-3i-A metal powder, Xl-Goo powder, Fe-In-Zn metal powder, Fe-Ni-Zn metal powder, Fe-Co-Ni-Cr metal powder, Fe-Co-N
1-P metal powder, Co-Ni metal powder and Co-P*
Examples include coarse powder, fine ferromagnetic metal powder, and the like.

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

Among these, preferred is fine Co-containing -Fe
20. It is a 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, BET angle is 4°121
(8 or higher) By using ferromagnetic powder, it is possible to easily realize a medium that allows high-density recording and has an excellent S/N ratio.

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

Examples of the functional group include =So, M, -0SO,
M, -COOM and OM+ (wherein M is a hydrogen atom or an alkali metal such as lithium or sodium, Ml and M2 are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group, and Ml and M2 may be the same or different.) is preferred.

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 working fluid is further improved, and 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 medium is also improved.

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

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 C or -C)12CCH2
S0ff, C-C112CH20SO□Y, CfL
-(:H2CO0M, 01lI'C sentence -C12-
It can be produced by condensing a compound such as P=00M2 (M, M', M2 have the same meanings as above) through a dehydrochloric acid reaction.

In the present invention, thermoplastic resins, thermosetting resins, electron beam curable resins, or mixtures thereof, which are conventionally known in the field of magnetic recording media, can be used as the binder. Alternatively, these may be used in combination with the modified resin.

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. Polymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester to ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl phthyral,
Cellulose derivative (cellulose acetate butyrate)
, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.)
, styrene phtadiene 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 diisocyanate prepolymers, urea formaldehyde resins, 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 in combination of two or more.

The amount of the binder in each magnetic layer is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the ferromagnetic powder.

If the amount of binder blended is too large, 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.

Next, in the present invention, a curing agent is used in combination with the binder.

Suitable examples of this curing agent include aromatic polyisocyanates and/or aliphatic polyisocyanates.

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 preferable.

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 blending amount of the curing agent with respect to the binder is as described above for the uppermost layer.

For magnetic layers other than the top layer, the amount of curing agent to the binder is usually 1/20 to 7/10, preferably 1/10 to 1/2, by weight.

In the magnetic recording medium of the present invention, for example, a lubricant and non-magnetic abrasive particles are added to the magnetic layer as necessary.

Various additive components such as conductive powder and surfactant can be included.

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 stearic acid) and a monohydric alcohol having about 3 to 26 carbon atoms.

Examples of the non-magnetic abrasive particles include alumina [
α-A x 2oz (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.
pm or less is better, and 0.4 lm or less is even better.

Incidentally, when the lubricant and nonmagnetic abrasive particles are contained particularly in the uppermost magnetic layer, the contact characteristics with the head (sliding performance, wear resistance, etc.) can be 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 preferably in the range of 5 to 100 m.

The surfactant is a natural type or a nonionic type.

Examples include anionic, 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.

There is no particular limit to the thickness of each magnetic layer, but the thickness of the top layer is 0.1 to 1.5 μm, and the thickness of layers other than the top layer is 0.1 to 5.0 μm.
A range of OILm is preferred.

- 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, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamide,
Plastics such as polycarbonate, Cu, AfL,
Metals such as Zn, glass, boron nitride, Si carbide,
Examples include ceramics.

There is no particular restriction on the form of the non-magnetic support, and it is mainly tape-like,
There are film, sheet, card, disk, and drum shapes.

The thickness of the non-magnetic support is not particularly limited, but in the case of a tape, film, or sheet, it is usually 3 to 100 mm.
The final length is preferably 5 to 50 ILm, and in the case of a disc or cart shape, it is usually 30 to 10 Pm, and in the case of a tram, it is determined as appropriate depending on the recorder etc.

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

Further, this nonmagnetic support may be subjected to a surface treatment such as a corona discharge treatment.

-Manufacture of magnetic recording medium- There is no particular restriction on the manufacturing method of the magnetic recording medium of the present invention, and it can be manufactured in accordance with the manufacturing method of a known multi-layer structure type magnetic recording medium.

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

Examples of the solvent include acetone, methyl ethyl ketone (MEK), and 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 types such as ethylene glycol monoacetate: Ether types such as ethylene glycol cimedylether, 2-ethoxyethanol, tetrahydrofuran, and dioxane: Aromatic hydrocarbons such as benzene, toluene, and xylene: Methylene chlorite, ethylene chloride tetrachloride Halogenated hydrocarbons such as carbon chloroform, ethylene chlorohydrin, and dichlorobenzene can 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.

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

Examples of this mixer include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller dispersion machine, a high-speed stone mill, a high-speed impact mill, a disper kneader-2 high-speed mixer homogenizer, and a super-high-speed mixer homogenizer. Examples include sonic dispersers.

Application methods include, for example, a wet-on-wet method, a wet-on-dry method, and a dry-on-wet method. et)
Method, dry-on-dry
Examples include methods.

Among these, the wet-on-wet method and the wet-on-dry 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 strengthens the adhesion between the upper and lower layers and smooths the surface of the magnetic layer.

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

FIG. 2 shows the above process, in which the non-magnetic support 5 unwound from the roll 4 is coated with a magnetic paint by the coating device 6, and then coated with the magnetic coating material by the first-stage magnetic field orientation device M7 and the second-stage magnetic field orientation device 8. After being processed (for example, zoooc) and further passed through a drying device 9, it is subjected to a surface smoothing treatment in a 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] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

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

(Examples 1 to 5. Comparative Examples 1 to 3) 1LHI reduction] Ferromagnetic powder (Go -y-FC20*, BET m5
5m2/g) 100 parts Vinyl chloride copolymer 13 parts (contains epoxy group and sulfonic acid metal base) Bowurethane resin
...8 parts (aromatic polyester) Stearic acid...2 parts Butyl stearate...2 parts Carbon black (average particle size 404m) ......3 parts alumina dispersion alumina (spherical particle size 0.2 gm)...6 parts polyurethane (aromatic polyester)...1 part methyl ethyl ketone-toluene-cyclohexane 1:1:1g compound - 7 parts Each component of the above two-layer composition, except for the alumina dispersion, 14 parts of methyl ethyl ketone and 14 parts of toluene are first dispersed, and then the above alumina is dispersed. The dispersion was added, and further 40 parts of methyl ethyl ketone, 40 parts of toluene, and 60 parts of cyclohexane were added, and the mixture was dispersed by sand milling.

Trifunctional isocyanate (the amount added is the first
), 45 parts of methyl ethyl ketone, 45 parts of toluene, and 40 parts of cyclohexane were added, thoroughly kneaded, and passed through a filter to obtain magnetic paint A.

``111'' (ferromagnetic powder (Go -y -FezO3, BET value 40m
2/g... 100 parts alumina (particle size 0.
1pm spherical)... 5 parts vinyl chloride copolymer...
... 17 parts (Nippon Zeon ML'1LlO) Polyurethane resin (contains sulfonic acid metal base) ... 13 parts Stearic acid ... 1 part Butyl stearate ... ... 1 part carbon black (particle size 201
Lm)... 3 parts Each component of the above lower layer composition, 12 parts of methyl ethyl ketone and 12 parts of toluene were first kneaded, then 88 parts of methyl ethyl ketone, 88 parts of toluene and 100 parts of cyclohexane were added and thoroughly dispersed. After that,
A trifunctional isocyanate was added and the mixture was passed through a filter to obtain magnetic paint B.

next,! i1 dense extrusion coater (FEC)
The magnetic paints A and B were simultaneously coated on a polyester base (film form) with a thickness of 13 gm so that the upper layer had a thickness of 0.54 m and the lower layer had a thickness of 4.4 pm.

Next, before the paint film dries, apply 2.00 g in the solenoid.
After magnetic field orientation at 00e, calender treatment was applied, and then paint C consisting of the following back coat composition was applied to the back side of the above polyester base until the thickness of the coating film after drying was 0.
．． The film was coated to a thickness of 6 μm to obtain an original fabric.

Then, one portion of this original fabric was slit into a 2-inch width to obtain a sample tape.

Back coat carbon black (particle size 22mg)... 1000
0 parts Carbon fluff diameter 75 m p-) 10 parts Calcium carbonate powder (particle size 130 parts) 10 parts Nitrocellulose 40 parts (Asahi Kasei Co., Ltd.) Made by Seltsuba BT) II/2) Polyurethane resin...
... 50 parts (N 3141 low molecular weight type manufactured by Nippon Polyurethane Co., Ltd., MW 50,000, hydroxyl group, urethane main chain contains 2
Polyisocyanate compound...15 parts (Coronate 3041) Cyclohexane...275 parts Methyl ethyl ketone...500 parts Toluene...
・・・・・・・・・・・・ Make 50 passes in the SOO club run.

The evaluation is O1 when the winding is not tight. If there is tightness, it is marked as ×.

(Hereinafter, blank space) The performance of the thus obtained sample tape was measured in the following manner.

The results are shown in Table 1.

(a) Cloudiness test After running the tape for 1 hour in an environment with a temperature of 20° C. and a humidity of 20%, the head was removed and observed under a microscope.

The evaluation was O: No cloudiness, Δ: Slight cloudiness or at an OK level, ×: Clear cloudiness.

And so.

(b) Sliding noise is expressed as a value with respect to a reference tape at 8 MHz using 10 buses of video technology.

(c) Tightness of winding during curing The entire length of the tape is maintained at a temperature of 40°C and humidity of 80% [Effects of the invention] According to the magnetic recording medium of the present invention, clouding, sliding noise, and tightness of winding can be effectively reduced at the same time. Something comes up.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the magnetic recording medium of the present invention.
(A) shows an example of a magnetic layer or a two-layer structure, and (B) shows an example of a magnetic layer or a three-layer structure. FIG. 2 is a process diagram showing an example of the manufacturing process of the magnetic recording medium of the present invention. S... Nonmagnetic support, 1... First magnetic layer, 2...
second magnetic layer, 3... third magnetic layer, 4... roll, 5
. . . Non-magnetic support, 6. Coating device, 7. First stage magnetic field orientation device, 8. Second stage magnetic field orientation device, 9. Drying device, 10. Super calender device, 11.・
·roll.

Claims (2)

[Claims] (1) In a magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, the weight ratio of the curing agent to the binder contained in the top layer is higher than that of the binder contained in the magnetic layers other than the top layer. A magnetic recording medium characterized in that the weight ratio is equal to or lower than that of the agent. (2) The magnetic recording medium according to claim 1, wherein the weight ratio of the curing agent to the binder contained in the uppermost layer is 50% or less.