JPS63209022A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having small surface electric resistance and excellent durability by incorporating two kinds of carbon blacks having average particle sizes in a specific range and having different oil absorptions at adequate weight ratios into said medium. CONSTITUTION:The carbon black A having 20-40mmu average particle size and 50-80cc/100g oil absorption and the carbon black B having 20-40mmu average particle size and 100-200cc/100g oil absorption are incorporated into the magnetic layer at A:B=5:5-1:9 weight ratios. At least a polyurethane resin contg. a sulfonic acid metal base is further incorporated as a binder component into said layer. The surface resistance of the magnetic recording medium is thereby maintained low without degrading the characteristics; in addition, the dispersibility and coating compd. aptitudes are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to magnetic recording media for recording information such as audio and video tapes and floppy disks.

(Prior art) Magnetic BeX bodies are magnetic powders, each! A magnetic layer is formed by uniformly dispersing the i additive in a binder resin and then coating and binding it onto a substrate such as a polyester film. This magnetic layer has a surface electrical resistance of 10'
' ~ 10" O/cJ, which makes it easy to save electricity, and static electricity causes dust in the air to accumulate and cause dropouts. To prevent this, carbon black is added to the magnetic layer as an antistatic agent. A method of containing is generally adopted.Usually, the average particle diameter is 20 to 40 mμ, and the oil absorption amount is 50 mμ.
~80 oe/100 g of carbon black, which has relatively good 4ffl properties, is added in an amount of 10 to 20% by weight to the magnetic powder to reduce the surface electrical resistance to about 106 to 109 Ω/d.

In recent years, as the density of recording media has increased, the thickness of the magnetic layer has tended to decrease, and as a result, it has become difficult to maintain the surface electrical resistance of the magnetic layer below 10@Ω/cJ with the conventional additive amount. became. Two methods have been considered for lowering the electrical resistance: adding a large amount of carbon black, which has relatively good conductivity, and adding an appropriate amount of carbon black, which has very good conductivity.

(11 RF Points to be Solved by the Invention) When a large amount of carbon black is added, the amount of magnetic powder and binder in the magnetic layer is relatively reduced, leading to deterioration of sensitivity, reproduction output, and durability. In addition, a method of adding an appropriate amount of carbon black with very good tetraelectricity (Japanese Patent Publication No. 57-1729)
0>, it is true that a small amount of addition is very effective, but since it is porous, it absorbs a lot of oil and binder components and solvents are easily adsorbed.As a result, the obtained magnetic paint becomes more chicken-like and thin ( It was difficult to uniformly apply the magnetic layer.Also, this is likely due to the porous nature of the carbon particles, which are intricately intertwined with each other, making it difficult to uniformly disperse the carbon particles, and the amount of time required for dispersion was It took a very long time (and the workability was poor).

Furthermore, carbon black usually has an average particle size of 50
Since it is the finest of the recording medium components, with a particle diameter of less than mμ, it is difficult to uniformly disperse it with conventional binder components, and the adverse effects of undispersed matter on the surface properties and electromagnetic characteristics of the magnetic layer become more pronounced as the film thickness decreases. It's here.

(Means for Solving the Problems) The present inventors have developed various types of carbon black in order to maintain the surface resistance of the magnetic recording medium as described above low without deteriorating its characteristics, and to titrate the dispersibility and coating suitability. As a result of studying binders, the present invention was arrived at.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing magnetic powder, a binder, etc. is coated on a non-magnetic support, in which the magnetic layer has (A) an average particle diameter of 20 to 40 m;
μ, carbon black with an oil absorption m of 50 to 80 cc/100 g, and (B) carbon black with an average particle diameter of 20 to 40 mμ and an oil absorption of ff1loo to 200 cc/100 g, with a weight ratio of A:l1=5:5 to 1:9. This is a magnetic recording medium characterized in that the magnetic recording medium contains the following:

Furthermore, the magnetic recording medium contains at least a sulfonic acid metal base-containing polyurethane resin as a binder component.

Average particle diameter 20 to 40 mμ, oil absorption f used in the present invention
As carbon black (A) with fi 50-80 cc/100 g, Mitsubishi #45. #52. (Mitsubishi Kasei) Regal 880,300 (Capoft),
Pr1ntex 300 (Dexa), Rav'en
1200, 1250 (=Roy Byan), etc. These carbons tend to reduce paint viscosity because of their relatively low oil absorption.

In addition, the average particle diameter is 20 to 40 mμ, and the oil absorption is 100 to 200.
For carb black (II) of cc / 100 g, Vulcan XC (Capot), Co
rax P (Dexa Corporation) conducte, xSC
, Conductex 975 (lO Biang Co., Ltd.), etc., and their main purpose is to lower the surface electrical resistance. The above carbon black No. 211 was used in order to titrate both coating suitability and surface electrical resistance.
:9, preferably at an ffl ratio of 4:6 to 2:8. If A is 5 or more, the dryness of the paste will be low, but the surface resistance will not be sufficient; conversely, if A is less than 1, the chicken coefficient will be large.

The amount of (A+B) is preferably 10 to 20% by weight based on the magnetic powder, and more preferably 12 to 18% by weight in terms of output and electromagnetic conversion characteristics.

The polyurethane resin used in the present invention has a ratio of 10 to 1000 equivalents ffl/10 of sulfonic acid metal base per polymer.
It is sufficient if it contains 'g. When the sulfonic acid metal base per polymer is less than 10 equivalents ffi/10'g, Br/8m
Not only cannot an increase in the value be expected, but at the same time it is not possible to obtain high packing properties of the magnetic particles. Moreover, if the amount of sulfonic acid metal base per polymer exceeds 1000 equivalents/10''g, the solvent solubility of the polyurethane resin will be poor and it will be impractical.

The polyurethane resin of the present invention is obtained by the reaction of a polyhydroxy compound and a polyisocyanate,
Part or all of the polyhydroxy compound contains a sulfonic acid gold scrap base.

As the polyhydroxy compound containing a sulfonic acid metal group, a polyester polyol containing a sulfonic acid metal group is particularly desirable. Polyester polyols with sulfo/acid metal bases consist of a carboxylic acid component without sulfonate metal bases, a glycol component, and a dicarboxylic acid component with sulfo/acid metal bases.

Examples of carboxylic acid components having no sulfonic acid metal base include terephthalic acid, isophthalic acid, orthophthalic acid, 1.
Aromatic dicarboxylic acids such as 5-naphthalic acid, Aromatic dicarboxylic acids such as P-oxybenzoic acid, P-(hydroxyethoxy)benzoic acid, etc. resinous dicarboxylic acids such as trimellitic acid, trimellitic acid, etc.
acids, tri- and tetracarbo/acids such as pyromellitic acid, and the like.

Glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-
Butanediol, 1,5-bentanediol, 116-
Hexanediol, Neope/Tyl Glycol, Diethylene Glycol, Jib[J-Bire/Glycol, 2,2.4
-) dimethyl-1,3-pebutanediol, 1,4-cyclohexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol,
Examples include polypropylene/glycol and polytetramethine glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and be/taerythritol may be used in combination.

Examples of dicarboxylic acid components containing sulfo/acid metal bases include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. The copolymerization amount of the dicarboxylic acid component containing these sulfonic acid metal bases is 0.5 mol% or more, preferably 1 to 50 mol%, based on the total carboxylic acid components.

There may be one type or 28 or more polyhydroxy compounds having the above-mentioned sulfo/acid metal base.

It may also be used in combination with polyhydroxy compounds that do not have sulfonic acid metal groups, such as ordinary polyester polyols, polyether polyols, acrylic polyols, castor oil derivatives, tall oil derivatives, and other hydrous acid group compounds.

The polyisocyanates used in the polyurethane resin of the present invention include 2.4-) Lyre/diisocyanate, 2.
．． 6-tolylene diisocyanate, P-phenylene diisocyanate, diphenylmethane diisocyanate, m
-Phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisonanate, 3.3
'-dimethoxy 4,4'-biphenylene diincyanate, 2,4-naphthalene/diincyanate, 313'
-dimethyl-4,4'-biphenylene diisocyanate)
, 4.4'-diphenylene diisocyanate, 4.4
'-Diisocyanate-diphenyl ether, 1.5
- naphthalene diisocyanate, p-xylylene/diisocyanate, m-xylylene diisocyanate), 1.3
-Diisocyanate methylcyclohexane 7.1.4-Diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diincyanate dicyclohexylmethane, inphorone diisocyanate, etc., but if necessary, 2,4 .4'
-) Reinocyanate-diphenyl, benzene triisocyanate, etc. can also be used in small amounts.

A polyurethane resin can be obtained by reacting a polyhydroxy compound and a polyincyanate in a solvent or in the absence of a solvent by a known method, and the desirable blending ratio is 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to 0.5 to (0.5 to 0.0 to It is 2/1. The molecular weight of the resulting polyurethane resin is preferably from aooo to 100,000.

In the present invention, other binders such as nitrocellulose, vinyl chloride copolymers, phenoxy, melamine resins, urea resins, etc. are used in combination with the polyurethane, as long as the dispersibility and durability are not impaired. I don't mind if you do. Particularly preferred are nitrocellulose, vinyl chloride copolymers, and phenoxy resins because they have the effect of improving wear resistance at high temperatures. In this case, the blending ratio is 10 to 200%, preferably 20 to 100%, and 200 to 200%, preferably 20 to 100%, based on the polyurethane resin of the present invention.
If it exceeds %, the film becomes brittle and its durability is impaired.

Furthermore, in the present invention, a resin that is compatible with the polyurethane resin of the present invention or the mixture of the polyurethane resin and nitrocellulose, vinyl chloride copolymer, or phenoxy resin is used within a range that does not impair the dispersibility of the magnetic powder. Adding, mixing, and/or a compound that reacts with a polyurethane resin or with a polyurethane resin, nitrocellulose vinyl chloride copolymer, phenoxy resin, etc.
and/or it is desirable to react. Examples of such compounds include epoxy resins, incyanate compounds, melamine resins, urea resins, and the like. Among these, incyanate compounds are particularly preferred. More preferred are polyisocyanate compounds containing two or more incyanate groups in one molecule. Specifically, Coronet L 1 day ■-summer manufactured by Nippon Polyurethane Co., Ltd.
L 1 E II, Millionaire) MT 1 Manufactured by Sumitomo Bay Urethane Co., Ltd.
Sumidur T80, 44S1 Desmodyur T65
, R1 Takeda Pharmaceutical Co., Ltd.) D102, 300S
etc. can be mentioned. These polyinsyanates can be used alone or 2i1! ffi or higher, and the amount added is preferably 5 to 0 OfftR%, based on the binder used in the present invention, since effective curing and crosslinking density can be obtained while the coating film does not become brittle. is 1
0-40mf2%.

The sulfonate/acid metal base "polyurethane resin has conventionally been very effective in dispersing magnetic powder, but it also showed good results in dispersing carbon black. This is due to the hydrophilic property of the sulfonate metal base. It is presumed that this effect also effectively acted on various functional groups on the surface of carbon black particles.

In the present invention, it is desirable to add fatty acids and fatty acid esters together as lubricants. Fatty acid esters are retained in the voids within the carbon black particles, giving good results in most cases. However, under hot and humid conditions, stable running may be difficult, perhaps due to the hygroscopic nature of carbon particles. In order to improve this, fatty acids may be added in combination.

The fatty acid preferably has about 10 to 18 carbon atoms, and specific examples thereof include lauric acid, myristic acid, palmitic acid, and oleic acid.

Examples of the fatty acid ester include incetyl stearate, tridecyl stearate, oleyl oleate, butoxyethyl palmitate, butyl laurate, and the mixture ratio of fatty acid: fatty acid ester is 10 to 4:6.
It is added in an amount of 2 to 10% by weight based on the magnetic powder.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to the Examples.

Example 1 lCo-7-Fe Os 100 parts (hereinafter, parts by weight) Sulfonic acid metal salt foundation Polyurethane resin 30 parts Nitrocellulose 10 parts α-AR, 0.3 parts Carbon black A (Raven 1200) Average particle diameter 24 mμ , oil absorption 55cc/100g
3 parts carbon black RL (Conductex S
C) Average particle size 20nl, oil absorption ffi 115cc
/100g 12 parts oleic acid
0.6 parts incetyl stearate 1.8 parts MEK 125 parts toluene
125 parts cyclohexanone
130 parts (The amount of sulfonic acid metal base in polyurecne resin containing sulfonic acid metal base is 378 equivalents/LO"
It is g. ) After dispersing the above components in a ball mill for 48 hours, 8 parts of Shibahashi agent (Coronet) L) was added, and the mixture was further mixed for 2 hours. After filtering the obtained magnetic paint, a magnetic layer with a dry film thickness of 1 μm was formed on a PET film with a thickness of 75 μm using a gravure method. After the surface treatment, it was left at 60° C. for 40 hours to undergo a sufficient hardening reaction, and then punched into 3.5-inch pieces and assembled into a 3.5-inch floppy disk. The performance of the obtained disk is shown in the table.

Examples 2 and 3 Table 1 shows the performance of samples obtained in the same manner as in Example 1, except that the amount of Raven 1200/Conductex SC added was 4/16° and 10/10.

Example 4 Table 1 shows the performance of a product obtained in exactly the same manner as in Example 1, except that 30 parts of Nifboran 2304 (Nippon Polyurethane Co., Ltd.), which does not contain a sulfonic acid metal base, was used as the polyurethane/resin.

Comparative Example 1 Table 1 shows the performance of a product obtained in exactly the same manner as in Example 1, except that 25 parts of 12 aven 1200 and 2.4 parts of incetyl stearate were used.

Comparative Example 2 18 parts of Conductex SC only, 0.
Table 1 shows the performance of C obtained in exactly the same manner as in Example 1 except that part G, 0.6 parts of imacetyl stearate and [...].

The surface electrical resistance is measured using a super insulation resistance diameter of 4329A manufactured by Yokogawa Hi, Neilet Puff Card Co., Ltd., and a resistivity measurement electrode of 1e00.
8A, and the squareness ratio and residual magnetic flux density were measured using a vibratory measuring magnetometer DI-mV-30 manufactured by Riken Denshi.

(Effects of the Invention) As described above, according to the present invention, a paint having excellent properties as a magnetic paint for use in magnetic recording media aimed at increasing density by thinning the magnetic layer can be obtained. The resulting magnetic recording medium has low surface electrical resistance and is highly durable.

Claims (2)

[Claims] (1) In a magnetic recording medium formed by coating a magnetic layer containing magnetic powder, a binder, etc. on a non-magnetic support, the magnetic layer has (A) an average particle diameter of 20 to 40 mμ, an oil absorption of 50 to 8
0cc/100g of carbon black and (B) average particle diameter of 20-40mμ, oil absorption of 100-200cc/100
A magnetic recording medium comprising: g of carbon black in a weight ratio of A:B=5:5 to 1:9. (2) The magnetic recording medium according to claim 1, wherein the binder is a polyurethane resin containing a sulfonic acid metal base.