JPH0687297B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having improved characteristics such as output, adhesive property, friction coefficient, still durability and head wear.

[Conventional technology]

Conventionally, for magnetic recording media such as audio tapes, video tapes, computer tapes and magnetic disks,
It is mainly used that a magnetic layer in which ferromagnetic fine powder such as ferromagnetic iron oxide or ferromagnetic alloy powder is dispersed in a binder is provided on a non-magnetic support.

[Problems to be solved by the invention]

Recently, with the development of technology in this field, there has been a demand for higher density and higher performance of magnetic recording media, and in particular, binders having good abrasion resistance and weather resistance have been developed as binders used for magnetic layers. For example, polycarbonate polyurethane resin (for example, JP-A-58-60430, JP-A-60-13324, and JP-A-61-9830).
JP-A No. 61-253627) and polar group-containing vinyl chloride vinyl acetate resin (JP-A-61-253627).

However, even with the use of these binders, although partial improvement in properties can be achieved, the output, adhesive strength, and
It is not enough to comprehensively improve wear resistance (friction coefficient), head wear, and the like, and development of a technique capable of improving such comprehensive performance is desired.

Therefore, an object of the present invention is to provide a magnetic recording medium having improved overall performance as described above.

[Means for solving problems]

The present inventor has conducted extensive studies to achieve the above object, and has found that the object can be achieved by the present invention described below.

That is, the present invention provides a magnetic recording medium in which a magnetic layer in which ferromagnetic fine powder is dispersed is provided on a non-magnetic support, wherein the magnetic layer is a polycarbonate polyurethane resin and a side chain thereof is a sulfonic acid group, a phosphoric acid ester group or a carboxyl group. Containing a vinyl chloride resin having at least one polar group selected from an amino group, an amino group and a hydroxyl group as a binder,
The magnetic recording medium is characterized by containing 3.0 to 5.0 parts by weight of an abrasive having an average particle size of 0.25 to 0.45 μm and a Mohs hardness of 6 or more per 100 parts by weight of ferromagnetic fine powder.

Hereinafter, the present invention will be described in detail.

Examples of the polycarbonate polyurethane resin used in the present invention include the above-mentioned polycarbonate polyester polyurethane (JP-A-58-60430) and polycarbonate polyurethane (JP-A-59-198530, JP-A-60-13324), and all bonds Used in the range of 10 to 90% by weight of the agent.

The polycarbonate polyester polyurethane used in the present invention is a polyurethane composed of a polyol, a polyisocyanate, and, if necessary, a chain extender, and the polyol is a polycarbonate polyol or a polyester composed of 1,10-decanedicarboxylic acid and a polycarbonate polyol. It is a polyol. The polycarbonate polyol used here can be obtained by condensation of a polyhydric alcohol with phosgene, chloroformic acid ester, dialkyl carbonate, diallyl carbonate or the like.

Further, as the polyhydric alcohol, 1,10-decanediol, 1,6-hexanediol, 1,4-butanediol,
1,3-butanediol, neopentyl glycol, 1,5-
Examples include pentanediol.

Further, as the polyisocyanate to be reacted with the above polyol, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, 1,5-naphthylene diisocyanate, hexamethylene diisocyanate, o-tolylene diisocyanate and these isocyanates There are addition compounds with active hydrogen compounds.

Examples of the chain extender used according to the above need include the above-mentioned polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like.

Further, the polycarbonate polyurethane used in the present invention is a polyurethane obtained by a urethanization reaction of a polycarbonate polyol and a polyvalent isocyanate,
The polycarbonate polyol and polyvalent isocyanate used here are the same as those mentioned above for the polycarbonate polyester polyurethane.

At the time of urethanization, other polyhydric alcohols and known chain extenders may be used in combination.

Polycarbonate polyurethane used in the present invention, in a nitrogen atmosphere, the polyol and polyisocyanate, the catalyst, if necessary, the presence of solvents such as amide-based, sulfoxide-based, cyclic ether-based, ketone-based, glycol ether-based It can be produced by heating below to 60 ° C. to 100 ° C. for several hours to prepare a prepolymer, and further reacting at the same temperature for several hours.

The vinyl chloride-based resin used in the present invention is a copolymer of vinyl chloride and another monomer that is polymerizable with vinyl chloride, such as vinyl acetate, vinylidene chloride, acrylonitrile, styrene, and acrylic acid ester. Groups, phosphate groups, carboxyl groups, hydroxyl groups, and epoxy groups are attached. The number average molecular weight of this vinyl chloride resin is preferably in the range of 15,000 to 60,000. The vinyl chloride content of this resin is 80-90wt%,
Other copolymerizable components of 20 to 10 wt% are preferred. Also,
The above polar group is 0.1 ~ 2.0wt% to vinyl chloride resin
Are bonded to the vinyl chloride resin. The epoxy group is 0.2 to 2.7 wt% with respect to the vinyl chloride resin, preferably 0.7
About 2.2 wt% is bonded to vinyl chloride resin.

Further, M of the —SO ₃ M group is selected from Li, Na, and K, but —SO ₃ Na is most preferable.

In the present invention, the total amount of the binder is 15 with respect to the ferromagnetic fine powder.
-50% by weight, preferably 20-40% by weight.

In the present invention, the above-mentioned polycarbonate polyurethane resin (A) and the polar group-containing salt (B) are contained in the magnetic layer, and the ratio thereof is (A) / (B) 90/10 to 10/90,
It is preferably 60/40 to 40/60.

In the present invention, a thermoplastic resin conventionally used together with the above polycarbonate urethane polycarbonate resin and vinyl chloride resin, if necessary, a thermosetting resin,
A reactive resin or a mixture thereof can be used.
These binders are described, for example, in JP-B-56-26890.

The abrasive particles having a Mohs hardness of 6 or more used in the magnetic layer in the present invention include α-alumina (α-Al ₂ O ₃ ), fused alumina, chromium oxide (Cr ₂ O ₃ ), corundum, silicon nitride, boron nitride, There are silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, etc., with an average particle size of 0.25 to 0.45 μm, especially
It is preferably 0.05 to 0.45 μm. Average particle size 0.45
If it is larger than μm, head wear becomes large, which is not preferable. Incidentally. The average particle size of the abrasive in the present invention is measured by an electron microscope.

The amount of abrasive particles added is preferably 0.1 to 20% by weight of the ferromagnetic powder.

Examples of the ferromagnetic material used in the present invention include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Fe.
Ox (1.33 <x ≤ 1.5), Fe metal fine powder, CrO ₂ etc. are available,
In particular, there are Co-containing γ-Fe ₂ O ₃ and Co-containing FeOx (1.33 <x ≦ 1.5). It is preferable that these ferromagnetic materials are powders having a particle size of about 0.1 to 1 μm. If desired, a lubricant and carbon black are further added to these magnetic layers,
Further, a plasticizer, a dispersant, a stabilizer and the like may be added depending on the purpose.

In order to manufacture the magnetic recording medium of the present invention using each of the above components, a coating solution having the composition described above is prepared, coated on a support, oriented, and then dried. Correspondingly, calendering or the like is performed to form the magnetic layer. In the coating liquid for forming the magnetic layer, each component is dissolved or uniformly dispersed in an organic solvent, and when coated on a support, any portion has a uniform composition.

As the organic solvent, alcohol solvents such as methanol, ethanol, isopropyl alcohol, butanol,
There are ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, acetone and cyclohexanone, and mixed solvents in which these are mixed in an appropriate amount ratio. These organic solvents are selected so that the components to be dissolved can be completely dissolved, and in the case of a mixed solvent, the quantitative ratio of each is appropriately determined together with the selection of the solvent. Further, these solvents should not deteriorate the characteristics of the ferromagnetic powder used as a component.

For dissolving the components in the solvent, it is usually preferable to use a dissolving machine equipped with a ball mill or a stirring blade.

The non-magnetic support used in the present invention is a plastic film having a large tensile strength, such as polyethylene terephthalate, cellulose triacetate, polyethylene naphthalate, polyamide and polyimide. The shape can be a desired shape such as a tape shape, a sheet shape, or a disk shape.

In the present invention, an undercoat layer (nonmagnetic layer) and a back layer may be further provided, if necessary.

〔Example〕

Hereinafter, the present invention will be described more specifically based on its examples. The measurement results of the samples in each example will be collectively described at the end. All "parts" in the examples are "parts by weight".

Examples 1 to 5 and Comparative Examples 1 to 4 Part of the following composition was put in a ball mill and sufficiently kneaded, and then the rest was put in a ball mill and sufficiently kneaded to give a desmodur L
7 parts of -75 (trade name of polyisocyanate compound manufactured by Bayer) was added and uniformly mixed and dispersed to prepare a magnetic paint.

γ-Fe ₂ O ₃ (Specific surface area 30 m ² / g) 100 parts Vinyl chloride-vinyl acetate compound Listed in separate table Polyurethane resin Listed in table Carbon black (average particle size 120 mμ) 10 parts Abrasive Listed in table Stearic acid 3.5 parts Solvent MEK / toluene / THF (mixing ratio 3/4/3) 200 parts Isocyanate compound 10 parts The polycarbonate polyurethanes used in Examples 1 to 3 and Comparative Examples 1 to 3 are those described in JP-A-60-13324. 1
The polycarbonate polyester urethane used in Example 2 was obtained in the same manner as in the synthesis example of the polycarbonate polyurethane in Example 1, and the polycarbonate polyester urethane used in Example 2 was obtained in the same manner as the synthesis example in Example 1 of JP-A-58-60430. Is.

As the polyester urethane used in Comparative Example 2, C-7209 manufactured by Dainippon Ink and Chemicals, Inc. was used. The composition of C-7209 is butanediol: adipic acid: tolylene diisocyanate =
It has a weight average molecular weight of 97,000 at 12: 11: 1 and a Tg of -30 ° C.

The magnetic tape prepared as described above was slit into a width of 1/2 inch, and the following evaluations were made to obtain the results shown in Table 1.

(Adhesive strength) Two sample tapes having an area of 1.27 cm × 2.5 cm = 3.18 cm ² were prepared by using a micro tablet molding machine manufactured by Hitachi, Ltd. Insert the glass plate between the spacers 2 and 2 so that the magnetic surfaces of 1 match each other, and apply pressure of 60 kg · cm to crimp. After holding at 50 ° C. for 5 hours, both tapes are stretched in the direction parallel to the surface with a tensile tester to measure the adhesive strength. The unit is kg / 3.18 cm ² .

When the binder hydrolyzes to lower the molecular weight, the pressure bonding
The magnetic surfaces adhere to each other, increasing the adhesive strength. That is, the adhesive strength indicates the adhesive property and the degree of hydrolysis of the binder, and it is desirable that this value be as small as possible.

(Measurement of dynamic friction coefficient) 50 g (T ₁ ) of the obtained video tape and stainless steel pole
The tension (T ₂ ) required to make the tape run at a speed of 3.3 cm / s under these conditions was measured. The friction coefficient μ of the video tape is calculated from this measured value.

μ = 1 / π ・ lnT ₂ / T ₁ (still characteristic) Video signal of image signal 50IRE is recorded, reproduced in still mode, and the reproduced RF output level is recorded by a recorder. It measured the time until it fell to 100.

(Glossiness measurement method for the magnetic layer surface) According to JISZ 8741, the refractive index is 1.567 at an incident angle of 45 °.
The specular gloss of the glass surface was measured as 100%.

(Output) The relative value when the ferrite head was used for the video tape recorder V500D manufactured by Toshiba Corp. and Comparative Example 1 was set to 0 dB is shown.

(Head wear) Using a ferrite head for Toshiba Corporation video recorder V500D, the obtained video tape was repeatedly run,
The amount of head dirt and head wear was measured after running for 100 hours.

In order to confirm the effect of stability over time of the present invention, the adhesive strength, the coefficient of friction, and the still durability are those after thermoaging (one left at 60 ° C. and 80% RH for 7 days). Was also tested and the results of both were compared.

In the above table, the unit of adhesive strength is (Kg / cm ² ), the unit of still durability is (minutes), and 60 ′ ↑ means 60 minutes or more.

(Effect of the invention) As is clear from the above results, according to the present invention, the magnetic layer contains a polycarbonate urethane and a polar group-containing vinyl chloride resin as a binder, and the average particle size is 0.25 to 0.
By including an abrasive with a Mohs hardness of 6 or more of 45 μm, it is possible to obtain a magnetic recording medium with excellent overall performance such as excellent gloss, output characteristics, friction coefficient and still durability, and low adhesive strength and head wear. it can.

[Brief description of drawings]

FIG. 1 is a schematic view showing an apparatus used to measure the adhesive strength in an example of the present invention. 1 …… Sample tape 2 …… Spacer 3 …… Torque

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshio Kawamata 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd. (56) Reference JP-A-61-222027 (JP, A) JP Sho 61-158023 (JP, A) JP-A 61-273735 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer having ferromagnetic fine powder dispersed on a non-magnetic support, the magnetic layer comprising a polycarbonate polyurethane resin and a side chain having a sulfonic acid group, a phosphoric acid ester group or a carboxyl group. Group, an amino group, and an abrasive having a vinyl chloride resin having at least one kind of a polar group selected from a hydroxyl group as a binder and having an average particle size of 0.25 to 0.45 μm and a Mohs hardness of 6 or more, A magnetic recording medium comprising 3.0 to 5.0 parts by weight based on 100 parts by weight of ferromagnetic fine powder.