JPS6234327A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent wear resistance and durability in a wide temp. range by using a specific binder as a binder for magnetic powder. CONSTITUTION:The binder which consists of a polyurethane resin and nitrocellulose and an aliphatic or alicyclic polyisocyanate compd. and has 30-150% breaking elongation of the binder at 0-50 deg.C is used as the binder for the magnetic recording medium constituted by coating a magnetic coating compd. contg. the magnetic powder and binder on a nonmagnetic base. The polyurethane resin contg. >=20wt% polyurethane resin having <=0 deg.C glass transition temp. is used. The polyurethane resin contains the metallic base of sulfonic acid at 10-1,000 equiv./10<6>g per polymer. The nitrocellulose compounded with the binder contributes to prevent the softening of the binder at a high temp., the increase of the elongation of the binder and the decrease of the modulus of elasticity thereof, thus improving the characteristics for the high-temp. use of the magnetic recording medium. The wear resistance and durability of the magnetic recording medium are improved by specifying the breaking elongation of the binder to 30-150%.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention uses a binder that has excellent dispersibility of magnetic powder and exhibits extremely little change in elongation over a wide temperature range. Concerning magnetic recording media that are known for their wear resistance and durability.

(Prior art) Conventionally, as a binder, for example, a plasticized vinyl chloride-vinyl acetate copolymer, a mixture of a polyurethane resin and a vinyl chloride-vinyl acetate copolymer, or an acrylonitrile-butadiene copolymer is used as a polyisocyanate. A cross-linked product is used.

(Problems to be Solved by the Invention) In the conventional technology using the above-mentioned binder, the elongation and elastic modulus of the binder often change significantly due to changes in temperature. It had the disadvantage of being inferior.

In other words, at high temperatures, the binder softens and becomes easier to stretch, increasing the friction coefficient of the magnetic layer of the magnetic recording medium and causing too much friction between the magnetic recording medium and the magnetic head, making it unusable in extreme cases. becomes.

In order to improve this, there are ways to reduce the amount of plasticizer used or increase the amount of polyisocyanate compound added to reduce the elongation of the binder at high temperatures. However, in this case, even if the high elongation at high temperatures can be improved, the elongation at low temperatures becomes too low at the Ni end, making it brittle, and the magnetic powder may fall off due to friction with the magnetic head. This will cause serious damage.

On the other hand, in order to improve the dispersibility of magnetic powder, conventional methods include adding a dispersant such as lecithyl, and using magnetic powder such as nitrocellulose, phenoxy resin, or vinyl chloride-vinyl acetate copolymer as a binder. There was a method of using a relatively thick dispersant (11) with a resin that has a relatively weak affinity for dispersants.However, when using this dispersant,
Because the dispersant is a low-molecular substance, it may bloom depending on the environmental conditions. In addition, since it acts as a plasticizer for the binder, the elongation of the binder increases at high temperatures, which increases the coefficient of friction. On the other hand, if a large amount of resin, such as dito-1 cellulose, is used, which has a relatively weak affinity with magnetic powder, the dispersibility will be improved, but the elongation of the binder at low temperatures will become too low. Even at room temperature, the magnetic layer becomes brittle or the adhesion with the non-magnetic base material deteriorates, resulting in problems such as separation.

A number of binders have been proposed that have been conventionally used in magnetic recording media, but they have the above-mentioned drawbacks. Therefore, they have to have appropriate elongation over a wide temperature range and do not change in temperature. We used a binder that satisfies good abrasion resistance and durability within a certain range, as well as good magnetic properties with excellent dispersibility of magnetic powder. No magnetic recording medium has been proposed yet.

In order to solve this problem, the present applicant did not invent a polyurethane resin that has excellent dispersibility of magnetic powder and excellent adhesion to non-magnetic substrates, but filed an application (Japanese Patent Application No. 53-08459).
)did.

When the polyurethane resin of the invention (Japanese Patent Application No. 53/06459) is used as a binder, a low molecular weight dispersant is not required, and it is convenient to obtain a magnetic recording medium having various advantages. However, the elongation tends to become too high at high temperatures, and it is still insufficient to obtain a magnetic recording medium with good durability at both low and high temperatures, which is the objective of the present invention. It had a point.

(Means for Solving the Problems) The present inventors have achieved excellent durability over a wide temperature range by combining specific binders and by making the elongation properties of the binders constant. It was discovered that a magnetic recording medium can be obtained.

That is, the present invention provides a magnetic recording medium in which a magnetic paint containing magnetic powder and a binder is coated on a non-magnetic substrate, in which the binder is a polyurethane resin, nitrocellulose, and an aliphatic or alicyclic polyisocyanate compound. The elongation at break of the binder is 3 at 0 to 50°C.
It is a magnetic recording medium characterized in that the polyurethane resin has a glass transition temperature of 0 to 150%.
The above magnetic recording medium contains 20% by weight or more of the following polyurethane resin, and further contains 10 to 1000 equivalents Q/10''g of sulfonic acid metal base per polymer as the polyurethane resin. Polyurethane N4 Ji used in the present invention includes polyurethane resins made from polyester polyol and polyisocyanate, polyurethane resins made from polyether polyol and polyisocyanate, etc., and the molecular weight and composition thereof can be selected to meet the needs of the present invention and claims. That is, a polyurethane resin having an elongation of 30 to 150% at 0 to 50°C is used as a binder from nitrocellulose and aliphatic or alicyclic polyisocyanate.

Furthermore, the polyurethane resin has a glass transition temperature of 0°C.
20 ffi of polyurethane resin: KL%
A polyurethane resin containing the above components is used.

The polyurethane resin containing a sulfonic acid group used in the present invention refers to a polyurethane resin containing 10 sulfonic acid metal groups per polymer.
~1000 equivalents/lo'g content is better if it is less than 1. 10 sulfonate gold ry4m groups per polymer f+t/I
If it is less than O"2, not only cannot an increase in the I3 r/nm value be expected, but also high packing properties of the magnetic particles cannot be achieved at the same time. In addition, if the amount of sulfur and monophosphate metal base per polymer is 1000 If ffi/10'g is exceeded, 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 used has a sulfo/acid metal base.

As the polyhydroxy compound having a sulfonate metal base, a polyester polyol having a sulfo/acid metal base is particularly desirable. Polyester polyols with sulfonate metal bases consist of a carboxylic acid component that does not contain sulfonate metal bases, a glycol component, and a dicarboxylic acid component with sulfonate metal bases.

Examples of carboxylic acid components without sulfo/acid metal bases include terephthalic acid, isophthalic acid, orthophthalic acid, 1.
Aromatic dicarboxylic acids such as 5-nuclic acid, P-oxyamp, aromatic acid, aromatic oxycarboxylic acids such as P-[hydroxyethoxy)benzoic acid, succinic acid, adipic acid, azerai/acid, sebacic acid, dodecane Resin group dicarboxylic acids such as dicarboxylic acids, trimellitic acid, trimesic acid,
Examples include tri- and tetracarboxylic acids such as pyromellitic acid.

Glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1.4 but/diol, 1.5-bentanediol, 1.6-hexanediol, neopendel glycol, diethylene glycol, dipropylene glycol, 2 , 2,4-trimethyl-1,3-be/diol, 1,4-Schif0
Examples include hexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethyl-1-lethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination.

Examples of the dicarboxylic acid component containing a sulfonate metal base include 5-sodium sulfoiphthalate, 5-potassium sulfoisophthalic acid, 2-sodium sulfoyl,! , terephthalic acid, 2-potassium sulfoterephthalic acid, etc.

The amount of copolymerization of the dicarboxylic acid component responsible for these sulfo/acid metal salts IJi is α5 mol% or more, preferably 1 to 50 mol%, based on the total carboxylic acid component.

There may be one type or 211 or more polyhydroxy compounds containing the di-sulfonic acid Kanai base.

It may also be used in combination with polynedroxy 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 their Sendai hydroxyl compounds.

The polyisocyanates used in the polyurethane resin of the present invention include 2.4-) lylene diincyanate, 2.
．． 6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m
-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate), 3.
3'-dimethoxy 4.4'-biphenylene/diincyanate, 2.4-naphthalene diisocyanate, 3.
3'-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! ,
4-Diincyanate methyl cyclohegyusan, 4.4'
-Diincyanate dicyclohexane, 4,4'-diincyanate dicyclohexylmethane, inphorone diisoleanate, etc.
．． .

Small amounts of 4'-triincyanate-diphenyl, benzene triisocyanate, etc. can also be used.

A polyurethane resin can be obtained by reacting a polyhydroxy compound and a polyisocyanate in a solvent or in an agent-free environment using a known method, but the desirable blending ratio is the NCO group of the polyisocyanate/01-1 group of the polyhydroxy compound. It is 0.5 to 2/l. The molecular weight of the resulting polyurethane resin is desirably from gooo to 100,000.

The magnetic powder used in the present invention includes γ-Pet O, Crow, cobalt 7, which has a spinel structure.
, T-light (Coo, Fe, O,) cobalt suction t7
iron oxide, ferromagnetic Pe-Co-Ni alloy, barium ferrite).

The nitrocellulose used in the present invention is not particularly limited, but preferably has a degree of nitrification of 5 to 20% and a degree of polymerization of 40 to 300, such as HI/2. HI/4. H2, Daicel Chemical's RS
I/2, RS I/4, R82, etc., and the amount used is preferably 2 to 100 parts by weight per 11 parts by weight of Boliureta 7 P411Fr.

The inclusion of nitrocellulose prevents the softening of the binder at high temperatures, the undesirable increase in the elongation of the binder, and the undesirable decrease in the elastic modulus, increasing the properties of the resulting magnetic recording medium several times in high temperature use. Contribute to. However, the addition of nitrocellulose causes an undesirable decrease in the elongation of the 1IIi mixture when the tolerance is low, so in order to prevent this, it is necessary to add 20% by weight or more of a polyurethane resin with a glass transition of 4 degrees below 0°C. ”-It is often necessary to use polyurethane containing In addition, in order for the binder to preserve properties that favor dispersibility, the sulfonic acid group
J? -Ata') 10"-1000ffi/10
It is often necessary to use polyurethane resins that are resistant to heat.

The aliphatic or alicyclic polyisocyanate compounds used in the present invention include hexamethylene diisocyanate), 4
．． 4'-diisocyanate ocyclohexylmethane,
Inholo/diisocyanate, tetramethylene diisocyanate, adducts and trimers of hexamethylene diisocyanate, adducts of trimethylolpropane and inholone diisocyanate, etc., but hexamethylene is especially suitable for reducing changes in elongation due to temperature. A trimer of diincyanate is preferred, and the mixing amount thereof is preferably 5 to 100 parts by weight per 100 parts by weight of the polyurethane resin. By using these polyisocyanate compounds, it is very easy to reduce changes in elongation due to temperature without depending too much on the composition ratio of the mixed system of polyurethane resin and nitrocellulose. A binder consisting of a mixed system of nitrocellulose and an aliphatic or alicyclic polyisocyanate compound has an elongation of 30 to 1 at a temperature of 0 to 50°C.
By using a binder that makes it 50%, low temperature (0℃)
Even in this case, the binder maintains appropriate elongation and elastic modulus and can prevent defects such as the magnetic layer being damaged by the head. At the same time, even at high temperatures (50°C), the dense three-dimensional crosslinking (1) structure of polyurethane resin - nitrocellulose - aliphatic, ring polyisocyanate compounds can prevent abnormal increases in the elongation of the binder. A magnetic recording medium that can prevent softening and has excellent durability and wear resistance can be obtained.

In the magnetic recording medium using the binder of the present invention, the binder may optionally contain other fibers such as ethyl cellulose. a
system resin, polyvinyl alcohol, polyvinyl butyral, polyvinidene chloride, vinyl chloride-vinyl acetate copolymer, acrylonitrile-butadiene copolymer,
Other resins such as styrene-butadiene copolymers may be blended as binders, but the blending amount must be selected so that the elongation at break at 0 to 50°C is 30 to 150%. If the elongation of the binder is less than 30%, the resulting magnetic layer will be too hard and brittle, and the wear resistance will be poor.
% or more, the coefficient of friction becomes large and both are impractical. In the present invention, in addition to the binder and magnetic powder, fine particles of carbon, fine particles of other tetraelectric substances, fine particles of inorganic substances such as gold fil oxide having a Mohs hardness of 6 or more may be added as necessary. . Furthermore, ultraviolet absorbers, oxidation stabilizers, and the like may be added as long as they do not impair the objectives and effects of the present invention. The non-magnetic ramming used in the present invention includes polymers such as polyesters typified by polyethylene terephthalate, polyphenylene sulfide, and other polymers alone or in blends, as well as other fibrous materials,
Films from these polymers containing particulate reinforcement,
Examples include tape and sheet-like materials.

The present invention will be specifically explained below using examples. "Example Middle" indicates parts by weight.

(Example) [1 Production of teriurethane resin] d! 582 parts of dimethyl terephthalate was placed in a reaction vessel equipped with a temperature of 111 °C, a stirrer, and a partial reflux condenser.
5 parts of dimethyl thorium sulfoisophthalate 21] 6 parts,
434 parts of ethylene glycol, 728 parts of neopentyl glycol, 0.66 parts of zinc acetate, 0.0 parts of sodium acetate
8 parts were added and the transesterification reaction was carried out at 140 to 220°C for 3 hours. Next, 1212 parts of sebacic acid was added, and 210 parts of sebacic acid was added.
After reacting at ~250°C for 2 hours, the reaction thread was depressurized to 205ml11g over 30 minutes, and further 5~20-11
1 g, and 'iRM synthesis reaction was carried out at 250°C for 50 minutes.

,? 5, the polynisdelpolyA-ru (A) is ηSP/
c=0.182, and had a hydroxyl number of 38. From NMR analysis and the like, its composition was as follows.

Terephthalic acid 30%, 5-sodium sulfoisophthalic acid 10 mol%, sebacic acid 60 mol%, ethylene glycol 44 mol%, neopentyl glycol 56 mol%.

A polyester polyol (n) was obtained in a similar manner. Its ηsp/c=0.130 and hydroxyl number were 49. Its composition is 80 mol% adipic acid, 5
-Sodium sulfoiphthalic acid 20 mol%, ethylene glycol 67 mol%, 1.5-bentanediol 33
mole%.

[Production of polyurethane resin]

Into a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, 1280 parts of toluene, 7850 parts of methyl isobutyl keto, 1000 parts of polyester polyol (A), 71 parts of diphenylmethane diisocyanate, and 1.2 parts of diptyltin silaurylate were added. It was made to react at 70-90 degreeC for 8 hours. The sulfonic acid metal base of the obtained 2-triurethane resin CI) is 378 m/10' g, molecule f
fi 1. There were 18,000 te. Polyurethane resin (n) was obtained in the same manner using 50 parts of polyester polyol (A) and 950 parts of polyester polyol (11). The content of sulfonic acid metal base is 365
equivalent/10'fir, and the molecular weight was 28,000.

The glass transition temperature is 28°C for polyurethane resin CI).
1 Polyurethane resin [■] was at -13°C. In addition,
Polyurethane resins (m) and (rV) were similarly produced using a polyester polyol containing no 5-sodium sulfoisophthalic acid. The glass transition temperature is (
I [I] was +30°C, and [■] was -19°C.

[Magnetic writing 1 medium! i! ! Construction and performance measurement of the binder film] ■ Prepare a magnetic paint with the following composition.

These were placed in a ball mill and mixed for 48 hours.

To this mixture was added 5.6 parts of Coronae EH (Nippon Polyurethane Co., Ltd.: 3ffi form of hexamethylene diinocyanate), and the mixture was mixed again in a ball mill for 2 hours. After filtration and defoaming, the thus obtained magnetic paint was applied to a polyethylene terephthalate film using a doctor blade with a 25μ gap, treated with a magnetic field, and then dried with hot air to perform surface treatment. Thereafter, a thermosetting treatment was performed at 60° C. for 7 days to sufficiently harden the magnetic layer. The thickness of the obtained magnetic layer was about 25μ. Obtained in this way,
Magnetic 3i! , g-media material was punched out to a size of 3.5 inches in diameter to make disks and their performance was evaluated. The results are shown in Table-1. In addition, the nitrocellulose, polyisocyanate compound, and polyurethane resin used in the above-mentioned magnetic paint were kneaded in the same composition, formed into a film cane, and then heat-treated at 60°C for 7 hours to fully cure the film. Stress at 0℃ and 50℃ respectively -
The strain characteristics were measured. The results are also shown in Table-1.

The following margins #tk 3, #yang 4, #captive 7 have glass transition temperatures of 0.
This was the case when polyurethane containing no more than 20% by weight of polyurethane resin at temperatures above 0°C was used, and the elongation at break of the binder filter at 0°C was 30% or less, resulting in poor disk performance.

In all other examples, the elongation at break at 0°C to 50°C was 30 to 150%, indicating excellent performance as a magnetic recording medium (disk), but among them, positive!
, Yang 2, Kang 8, and Sui 11 were better than Teeth 5, Yang 6, and lTh1O, with higher amounts of sulfonate-based polyurethane showing a tendency to be better binders. Ta.

The middle part of the table indicates that the magnetic layer was damaged or the drive stopped due to an abnormal increase in rotational torque, making measurement impossible.

In addition, the measurement was performed as follows.

- Durability: A continuous running test was conducted using a floppy disk drive in a constant temperature bath, and the output decrease (%) after 3 million bus cycles was measured.

- Breaking elongation: The measuring device used was Tensilon IJTM-ITI manufactured by Toyo Boldwy/G.A., and the film was measured to have a length of 101 cm and a width of I CI using a temperature controller.

The thickness was about 50μ, the measurement was carried out at a chuck gap of 41, a tensile speed a of 200 mm/min, and a chart speed of 500 m5/min.

(2) A magnetic recording medium was manufactured by the same method as in (2). At the same time, we created a film of the binder used at that time.
The elongation at break was measured. The performance of the magnetic recording medium and the elongation at break of the film were measured. Table 2 does not show the performance of the magnetic recording medium and the elongation at break of the film.

Below margin Note that in Table 2, a single mark indicates that no measurement was performed.

In Examples No. 1113 to 20, the binder of the present invention is composed of a polyurethane resin, nitrocellulose, and an aliphatic or ring polyisocyanate, and the binder has an elongation of 0" to 5.
This is a case where the ratio is 30 to 150% at 0° C., indicating that an excellent magnetic recording medium can be obtained. In comparison, Comparative Positives #21 to #26 contain no cellulose or aliphatic or cyclic polyisocyanate, and in both cases, the elongation of the film as a binder is 0°C. It was outside the range of 30 to 150% at ~50°C, and therefore only magnetic recording media of inferior quality could be obtained.

Claims (3)

[Claims] (1) In a magnetic recording medium formed by coating a magnetic paint containing magnetic powder and a binder on a non-magnetic substrate, the binder comprises a polyurethane resin, nitrocellulose, and an aliphatic or alicyclic polyisocyanate compound. Consisting of
The elongation at break of the binder is 30 to 150 at 0 to 50°C.
% magnetic recording medium. (2) The magnetic recording medium according to claim 1, wherein the polyurethane resin contains 20% by weight or more of a polyurethane resin having a glass transition temperature of 0° C. or lower. (3) The magnetic recording medium according to claim 1, wherein the polyurethane resin has 10 to 1000 equivalents/10^6 g of sulfonic acid metal base per polymer.