JPS6095723A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having an excellent electromagnetic converting characteristic and durability by using a binder which consists of a mixture composed of a polyurethane resin having specific modulus and a vinyl chloride-vinyl acetate compolymer at a specific compounding ratio and is added with polyisocyanate in forming a magnetic layer. CONSTITUTION:A magnetic paint prepd. by adding magnetic powder and a lubricating agent to a binder consisting of a mixture composed of a polyurethane resin having 50-100kg/cm<2> 100% modulus and a vinyl chloride-vinyl acetate copolymer resin at (50:50)-(90:10) weight ratio and polyisocyanate is coated on a nonmagnetic base and is dried. The coating is then subjected to a calender roll treatment and to specular surface finishing to manufacture a magnetic recording medium. The lubricating agent to be added is a mixture componed estess of higher fatty acid and alight, dibasic acid such as adipic acid having 40:60- 60:40wt. ratio or a mixture composed of ester of aliphat, monobasic acid such as stearic acid or the like as a part of esters. The magnetic recording medium having good dispersibility of the magnetic powder and having excellent mechanical strength, durability, etc. is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. The structure of conventional examples and their problems. Magnetic recording media such as magnetic tapes and magnetic disks are made of polyester, etc. It is constructed by providing a magnetic film made of magnetic powder and a binder on a support, and is required to have excellent electromagnetic conversion characteristics and high durability.

Generally, the electromagnetic conversion characteristics of a magnetic recording medium become better as the spacing loss decreases, so it is desirable that the surface roughness of the magnetic coating film is small. However, since the magnetic coating comes into violent sliding contact with the magnetic head during recording and playback, in order to obtain high durability it is necessary to minimize the frictional resistance of the magnetic coating. It is said that it is desirable to increase the roughness.

Conventionally, in order to improve the electromagnetic conversion characteristics of magnetic recording media, the smoothness of the surface of the magnetic coating film has been improved by, for example, sufficiently carrying out calender roll treatment or polishing treatment. The durability of the magnetic coating film tended to decrease as the surface smoothness of the magnetic coating became better.

In addition, in the past, in order to improve the durability of magnetic coatings, in addition to selecting the type of binder for forming magnetic coatings, lubricants were mixed in and relied on the surface smoothing effect. , a relatively large amount of lubricant was mixed in. However, the mixing of a large amount of such lubricant causes blooming on the surface of the magnetic coating film, which becomes sticky and causes pinholes to occur during calender roll treatment.

As described above, in the past, regarding the surface roughness of magnetic coating films, electromagnetic conversion characteristics and durability tend to contradict each other, and it has been difficult to satisfy both characteristics at the same time.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic recording medium that can improve the surface smoothness of a magnetic coating film, obtain excellent electromagnetic conversion characteristics, and at the same time satisfy its high durability. In the invention, as a binder, 100% modulus is 50~
It consists of a 100Kf/cd polyurethane resin, a vinyl chloride/vinyl acetate copolymer resin, and a polyisocyanate, and the weight/weight ratio of the polyurethane fiber and the vinyl chloride/vinyl acetate copolymer resin is 50:50 to 90:10. A magnetic recording medium uses a certain binder and has a magnetic coating film made of magnetic powder, a lubricant, and the binder provided on a support.

As mentioned above, the binder used in the present invention is composed of a polyurethane resin having a 100% modulus of 50 to 100 kg/afl, a vinyl chloride/vinyl acetate copolymer resin, and a polycincyanate.

Any commercially available polyurethane resin can be used as the polyurethane resin, but for example, trade names N-2304, N-2302, N-3022, I manufactured by Nippon Polyurethane Kogyo Co., Ltd.
'm-101 etc.

As a polyurethane resin, 100% modulus is 50~
Using 100Kf/cd polyurethane resin, 10
If the 0% modulus exceeds 100 Kg/cJ, the dispersibility of the magnetic powder and other optional components such as bands, anti-static agents, abrasives, etc. mixed into the binder becomes poor, and it is difficult to sufficiently disperse them using commonly used dispersion methods. When a magnetic coating film is formed, the surface roughness of the coating film becomes large, and excellent electromagnetic conversion characteristics cannot be obtained. Furthermore, if strong dispersion is performed, it will be 100K.
In some cases, it is possible to disperse magnetic powder using a polyurethane resin that exceeds g/cJ, but in this case, the coercive force (Ha
) decreases, which is undesirable.

Further, if a polyurethane resin having a 100% modulus of less than 50 kg/cJ is used, the mechanical strength of the magnetic coating film formed using this resin will be weakened and the durability will be deteriorated, which is not preferable.

In the binder used in the present invention, a vinyl chloride e vinyl acetate copolymer resin is used together with the above-mentioned polyurethane resin. Such vinyl chloride/vinyl acetate copolymer resins are commercially available, such as those manufactured by Union Carbide & e-Carbon under the trade names VAGH, VAGD,
There are YMCAs, etc.

In the binder used in the present invention, the important ratio of polyurethane resin and vinyl chloride/vinyl acetate copolymer resin is 5.
Use at a ratio of 0:50 to 90:10. If the proportion of the vinyl chloride/vinyl acetate copolymer resin increases outside of the above range, that is, if the proportion of the polyurethane resin decreases, the surface roughness of the formed magnetic coating film becomes large and the head output becomes low. Further, the magnetic coating becomes hard, the elongation at break decreases, and the durability becomes poor especially in a low-temperature, low-humidity atmosphere, which is not preferable.

Conversely, when the proportion of vinyl chloride/vinyl acetate copolymer resin becomes small, that is, when the proportion of polyurethane resin becomes large, the mechanical strength of the magnetic coating film formed becomes insufficient.
Durability deteriorates, which is undesirable. That is, the ratio of polyurethane resin to vinyl chloride/vinyl acetate copolymer resin is 50:
When the ratio is within the range of 50 to 90:10, sufficient smoothness can be obtained for the magnetic coating film by ordinary dispersion methods, and an excellent electromagnetic 1ff
It has been found that i4fi characteristics and high durability can be obtained at the same time.

Next, in forming the magnetic coating film of the present invention, a lubricant is mixed into the above-mentioned binder.

As the lubricant, conventionally used lubricants can be used, but in the present invention, it is preferable to use a mixture of higher fatty acids and aliphatic dibasic acids in a weight ratio of 40:60 to 60:40. It turns out.

Higher fatty acids that can be used include myristic acid, palmitic acid, stearic acid, and oleic acid. Further, usable aliphatic dibasic acid esters include dioleyl succinate, dioleyl adipate, dioleyl azelaate, and the like.

In the lubricant used in the present invention, the ratio of higher fatty acid to aliphatic dibasic acid ester is 40:60 to 50:5.
If it is within the range of 0, when performing calender roll treatment to form a magnetic coating film and improve surface smoothness, there will be little lubricant oozing out, no adhesion to the roll surface will be observed, and no formation will occur. It was found that the friction coefficient of the coated film was reduced and the durability was improved to more than 10 million passes.

On the other hand, if the proportion of higher fatty acids becomes large and the proportion of aliphatic dibasic acids becomes small outside of the above range, no adhesion of the lubricant to the roll surface is observed, but the coating film formed is This is not preferable because the coefficient of friction increases and durability deteriorates. In addition, when the proportion of higher fatty acids is small and the proportion of aliphatic dibasic acid esters is large, the friction coefficient of the magnetic coating film that is formed becomes small and the durability is improved, but it lubricates the calender roll surface during coating film formation. It is undesirable that the agent will stick to it.

Furthermore, by substituting a part of the aliphatic dibasic acid ester used in the present invention with an aliphatic-basic acid ester such as butyl stearate, butyl oleate and/or lauryl oleate, the compatibility with the binder can be improved. The ratio of lubricant used at low temperature and low T7 has been improved and can be made the same as the ratio of lubricant used in conventional magnetic coating formation.・In the binder used in the present invention, the polyurethane resin and vinyl chloride
Add 5 to 4.0 INfk parts of polyisocyanate as a resin component bridging agent for the vinyl acetate copolymer resin. □ Examples of such polyisocyanates include four products manufactured by Nippon Polymer Co., Ltd. (Coronet) LS□
Coronate HL etc. can be used:. By adding a resistant polyisocyanate, the strength of the magnetic coating film formed by resin □ during coating film formation can be greatly improved and excellent durability can be imparted. - In this case, if the amount of polyisocyanate added is less than 5 parts by weight, the mechanical strength of the formed coating film will be weakened, which is undesirable, and if it exceeds 40 parts by weight, the magnetic coating film will become brittle, which is not preferred.

The vine magnetic powder used in the present invention includes conventionally known magnetic iron oxide powders such as Fe, 0. .

CO-containing F's30. , 7-Fe, Os, Co-containing 7-Fe, 0. In forming the magnetic coating film of the present invention, known dispersants such as lecithin, known antistatic agents such as carbon black, Cr, O, Al, O, Known abrasives such as the like can be mixed.

Films and sheets made of polyester, polyacetate, polyimide, and polyamide can be used as supports for magnetic coatings.

Since the magnetic coating film according to the present invention uses a binder containing a polyurethane resin with a <100% modulus of 50 to 100 h/cl and a vinyl chloride/vinyl acetate copolymer resin as described above, there is no possibility of contamination in the binder. The dispersibility of the magnetic powder is extremely good, and therefore the surface smoothness of the magnetic coating film is good, and electromagnetic conversion characteristics such as head output and resolution are significantly improved. Furthermore, the durability of the magnetic coating film satisfies <10,000,000 passes/track or more, as shown in the Examples described below. Furthermore, since the binder of the present invention has excellent dispersibility with respect to magnetic powder, it is not necessary to use a special dispersion method, and a dispersion that provides sufficient smoothness can be easily obtained using ordinary dispersion methods such as crosstalk. I can do it.

For this reason, there is no need to improve surface properties using harsh calendering or polishing, which can easily damage the coating surface, as is done in conventional coating film formation. Magnetic coatings with conversion properties and high durability can be obtained. Furthermore, the binder used in the present invention exhibits appropriate mechanical strength and elongation at break against frictional force.
Therefore, even if the magnetic recording medium is deformed by frictional force, it is difficult to break, and by elongating to a certain extent, the frictional force is absorbed and alleviated, thereby improving durability.

Furthermore, the above-mentioned lubricant according to the present invention has good compatibility with the binder, good adsorption to fine powders such as magnetic powder and other additives such as carbon black, and no bleeding to the coating surface. It is believed that this method is suitable, does not cause excessive adhesion to the roll during calendering, lowers the coefficient of friction of the magnetic coating film formed, and provides excellent electromagnetic conversion characteristics and high durability. DESCRIPTION OF EXAMPLES The present invention will now be explained with reference to examples. In the examples, parts are parts by weight unless otherwise specified.

Example I 100 parts of Go-containing magnetic iron oxide powder, as shown in Table 1 below, were prepared using various polyurethane resins with different modulus and elongation at break (all of which are manufactured by Nippon Polyurethane Industries Co., Ltd. and have a trade name). 20 parts of vinyl chloride/vinyl acetate copolymer resin (manufactured by Union Carbide & Carbon, trade name: VAGH) (weight ratio of polyurethane resin to copolymer resin of about 71:28)
, 5 parts of stearic acid, 5 parts of dioleyl adipate, 2 parts of lecithin, 15 parts of carbon black, 4 parts of alumina powder, 80 parts of toluene, 80 parts of methyl ethyl ketone, and 80 parts of methyl isobutyl ketone. %, polyisocyanate (product name Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.)
) was added and mixed well, and the dried magnetic coating film was coated on a 75 fim thick polyester film with a thickness of 1.
It was spread on both sides to a thickness of 3" lit and dried.The surface of the magnetic coating layer was then treated with a calendar roll at 40°C to create a mirror-finished Tuppy disk. The roughness of the film surface and the electromagnetic conversion characteristics -
When the head output and durability were measured, the results shown in Table 1 were obtained.

Polyurethane resin N-3118, N-5032 in Table 1
, N''-5033, NR-9Q and N-2301 have a 100% modulus of wood Example 2 100 parts of Co-containing magnetic iron oxide powder, polyurethane resin (R-101) in the proportions shown in Table 2, and Vinyl chloride/vinyl acetate copolymer resin (VAGH) (D combination; f
t Mi2B parts, myristic acid 5 parts, butyl stearate 1 part, adipate dioleyl 4 parts, lecithin 2 parts, carbon black 15 parts, alumina powder 4 parts, toluene 8 parts
0 parts, 80 parts of methyl ethyl ketone and 7 parts of cyclohexane
280 parts of this polyisocyanate (Coronate L) were mixed as in Example 1 to form a mixture of 1"00iJN polyisocyanate (Coronate L).
A floppy disk was prepared in the same manner as in Example 1 using the magnetic paint prepared by adding 10 parts of the magnetic paint. The surface roughness, head output, and durability of each sample obtained were measured, and the results shown in Table 2 were obtained.

Example 3 100 parts of Co-containing magnetic iron oxide powder, polyurethane resin (
R-101) 20 parts, vinyl chloride-vinyl acetate copolymer resin (VAGH) 8 parts 1 total amount of stearic acid and dioleyl adipate in various proportions shown in Table 3, 10 parts,
2 parts of lecithin, 15 parts of carbon black, 4 parts of alumina powder, 80 parts of toluene, 80 parts of methyl ethyl ketone and 80 parts of methyl isobutyl ketone were mixed as in Example 1, and 100 parts of this mixture was mixed with polyincyanate (Coronet) L. ) A floppy disk was prepared in the same manner as in Example 1, using a magnetic paint prepared by adding 10 parts of . The dynamic friction coefficient, durability, and adhesion of lubricant to the calender roll surface of each sample obtained were measured. Under normal environment (25℃, 60%RH)
Continuous rotation was performed at a low temperature and low humidity (5'C, 140% RH) under the conditions of a pad pressure of 15fr and a rotational speed of 30 orpm, and the rotational speed is shown as the rotational speed until the playback output of the floppy disk becomes 70% or less of the initial output. .

The surface roughness of the coating film was measured with a surface roughness meter (manufactured by Rank Tiller Bobson) and expressed as root mean square roughness.

The head output was determined using a standard testing machine based on the standard for 3-inch compact floppy disks, with 2 f on track 39.
After recording the signal, the average signal amplitude when playing back is expressed as a voltage.

The 100% modulus and elongation at break were determined by adding 1 polyisocyanate (Coronate L) to each polyurethane resin.
After adding 0 phr and curing, a film with a thickness of about 100 μtn was created, and using a JI No. 84 dumbbell, 2
The stress and elongation were measured at 00+m/min.

The dynamic friction coefficient was measured with a cursor type dynamic friction coefficient measuring device (manufactured by Kyowa Kagakusha).

To check the adhesion of lubricant to the calender roll surface, apply magnetic paint to the support, then calender with a calender roll, visually observe the amount of lubricant adhering to the roll surface, and check if there is almost no dirt. , corresponding cases are indicated by ×.

Effects of the Invention As is clear from the above Examples and data thereof, a magnetic recording medium having a magnetic coating film formed using a binder according to the present invention and a magnetic paint containing a lubricant according to the present invention. This method has excellent effects in that the smoothness of the coating film surface is improved and excellent electromagnetic conversion characteristics and high durability are achieved at the same time, and its practical value is great.

Patent applicant: Matsushita Electric Industrial Co., Ltd. Adatsu Hikari, a representative Kai Yasuda Satoshi

Claims (1)

[Claims] 1. As a binder, the 100% modulus is 50 to 10.
Consisting of 0Kq/ca polyurethane resin, vinyl chloride/vinyl acetate copolymer resin and polyisocyanate,
Using a binder in which the weight ratio of the above polyurethane resin and vinyl chloride/vinyl acetate copolymer resin is 50:50 to 90:10, a magnetic coating film consisting of magnetic powder, a lubricant, and the above binder is applied onto a support. A magnetic recording medium characterized by being provided with. 2. The magnetic recording medium according to claim 1, wherein the lubricant comprises a higher fatty acid and an aliphatic dibasic acid ester in a weight ratio of 40:60 to 60:40. 3. The magnetic recording medium according to claim 2, wherein a part of the aliphatic dibasic acid ester is replaced with an aliphatic-basic acid ester.