JPS6010368B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the lubrication of magnetic recording media such as tapes, cards and disks.

As magnetic recording media advance, it is known that their recording surfaces should be lubricated to allow sliding contact with the recording head.

The first lubricants were fatty acids and esters such as carnoba wax. These are either added to the dispersion of magnetizable particles and binder resin or coated onto the final recording surface. This fatty acid and ester lubricant was considered satisfactory under normal atmospheric conditions, but was considered unreliable at high temperatures and high relative humidity, such as 40q0 and 80% relative humidity.
Modern flexible magnetic recording media have about 70% fatty acid and ester lubrication, and most others use silicone lubrication.

U.S. Patent Nos. 3,490,946 and 3,778,308 are
The use of elementary carbon compounds as a lubricant for magnetic recording media has been suggested, but these are rarely used as lubricants for steerable magnetic recording media. On the other hand, hard magnetic recording disks have one CaF2-○- unit (where a is 1 to 4
A fluorinated carbon, such as highly fluorinated polyethers, having a backbone consisting of ), n is an integer.

] is almost always lubricated. Such polymers are
It is commercially available as Krytox 143 from I. DuPont. A preferred member of this class has a Ferrantee-Shirley viscosity of 1322 centipoise and a viscosity index of 145 (ASTMD
2270) and "Krytox" 14 core, which is reported to have a number average molecular weight of about 7000. When these fluorinated polymers are used to lubricate hard disks, they tend to be removed when the disks are washed with inpropyl alcohol. The present invention relates to a magnetic recording medium, the magnetizable layer of which has 40
It has a lubricating coating that provides effective lubrication at 0.00 and 80% relative humidity.

When used to lubricate hard disks,
This lubricating coating is difficult to remove even when wiped with a cloth containing inpropyl alcohol. The lubricating coating of the present invention is one C8
F2a-○-unit (a is an integer from 1 to 4)
comprising a fluorinated telechelic polyether polymer having a backbone consisting of a fluorinated telechelic polyether polymer terminated with at least one polar group such that the 12/MW is at least 19 x 10-4 Deb 2-mol/unit. combined.

"Telechelic monopolymers have low molecular weights and known functional end groups. The dipolar moment of a fluorinated telechelic polymer can be calculated from the Onsager relation.

Mountain 2 = Water TMW (Gos - Go) (2 Gos + What) 4 Bamboo Nod Gos (Where + is, k = Boltzmann constant, T = Temperature, K MW = Molecular weight No = Avogadro number d = Density Gos = dielectric constant measured at low frequency, Goto = dielectric constant measured at high frequency, and where the main rule is Goto Nito D2 10 (5-10%) Katana.

2 1.075 ri.

2 (where o is 2p0, which is the refractive index of the material at the sodium D line).

The fluorinated telechelic polyether polymer preferably has a number average molecular weight of at least 1000 and a 7 erantiy Shirley viscosity (
1M current stage - measured at 1 and 20oo). The number average molecular weight of fluorinated telechelic polyether polymers having more than one terminal polar group per polymer molecule is preferably somewhat lower than that of telechelic polymers having only one terminal polar group. expensive. For example, if there are two terminal polar groups per polymer, the number average molecular weight is preferably 1500
exceed. Useful polar groups for fluorinated telechelic polyethers include -C02R, where R is alkyl of 1 to 6 carbon atoms, 6 to 1
aryl or alquaryl of 0 carbon atoms), (
However, each of R' and R'' is hydrogen, alkyl of 1 to 6 carbon atoms, benzine, or -R'''OH (R
... is an alkylene group of 2 to 6 carbon atoms)
, -CbH2b.

day, -CbH2bNR'R'', , or 1C(OH)2CbF2M (where b is an integer from 1 to 4).

Strongly acidic polar groups such as carboxylic acid or sulmic acid groups are
Less desirable as it can be corrosive. This can be converted into a salt by converting it into a salt.
Preferably, the pKa of the telechelic polyether polymer is
is at least 1.0. Preferred fluorinated telechelic polymers are those disclosed in U.S. Pat.
As in No. 85137, spine - [CF2CF20]
m-[CF20]n-, where m is an integer from about 6 to 32 and n is an integer from about 12 to 52, or the spine as described in U.S. Pat. - [CF(CF3)CF20chin or fCF2CF(CF3)○chin (where n is an integer of about 6 to 20). Such fluorinated telechelic polyethers have a number average molecular weight within the preferred range of 1000-5000 and a ferranty within the preferred range of 20-2000 centipoise. Shirley viscosity (1
640-1 seconds). This fluorinated telechelic polyether polymer is
Similarly increases the separation between ether oxygens, and above 1
It is necessary to avoid number average molecular weights towards the higher end of the preferred range of 000-5000 -CF2-CF
Contains 2-units. On the other hand, the viscosity of pyrinized telechelic bolyether polymers is too high to provide good lubrication. Excellent lubrication of maneuverable magnetic recording media is achieved by applying the fluorinated telechelic polyether polymer in a rotogravure coater from a 0.1% by weight dilute solution or emulsion; This results in what is believed to be a coating weight of approximately 9/10.

Such coatings are approximately monomolecular thick. The actual coating weight is very small and difficult to measure, but is approximately 10 to 1
Excellent lubrication is achieved with a coating weight believed to be 9' of 50. 0.4-
Applied from a 0.8% solution or emulsion, approximately 25-6
It is generally preferred to obtain a coating weight of 0.9'. This gives a reasonable guarantee of good lubrication properties under adverse environmental conditions for several years. The fluorinated telechelic polyether polymer is applied to the hard magnetic recording disk by wiping from a dilute solution or dispersion or by other techniques, such as by spraying or dipping.

After drying, the surface is dried and buffed with a soft tissue to distribute the lubricant and remove any excess. This polishing changes the appearance from slightly cloudy to shiny. When a 5r drop of n-decane after one feeding has a diameter of approximately 3 skins, this indicates that a continuous coating has been applied.

When no lubricant is present, the droplet diameter is approximately 10-1
It has two ribs. It is unknown how much lubricant was removed by polishing, and the coatings are so thin that it is difficult to measure their thickness. Since a monolayer of fluorinated telechelic polyether polymer is believed to be on the order of 40 angstroms thick, it is assumed that the coating is at least this thick. What about electron scattering measurements?
It has been suggested that a thickness of 5 to 250 angstroms gives favorable results. An unduly thick coating of fluorinated telechelic polyether polymer on a hard recording disk creates undue obstruction. For the purpose of providing reliable stop motion in videotape recorders at high temperatures and high relative humidity, it is desirable to blend the fluorinated telechelic polyether polymers with other lubricants such as fatty acids and esters.

The fluorinated telechelic polyether polymer should comprise at least 1% by weight of the blended boar agent. Preferably the coat weight of the blended lubricant is
25 to 150 females/me. The packing material for each of the magnetic recording media of Examples 1-8 was a flexible diagonally oriented polyethylene terephthalate film having a thickness of about 15 micrometers.

Example 1 A preferred fluorinated telechelic polyether polymer of the present invention is (where m and n are each integers giving an average molecular weight of about 2000) and has a Ferranti-Shirley viscosity of 1440. has.

0.3 hours of this telechelic polyether was emulsified in 60 hours of inpropyl alcohol, and the emulsion was applied with a rotogravure coater onto the recording layer of a flexible magnetizable coding tape.

The recording layer consisted of fine magnetizable iron oxide particles in a binder consisting of crosslinked polyvinyl chloride copolymer and polyester polyurethane. This recording layer was specifically designed for helical scan video recording, except that it is lubricant-free. After drying the telechelic polymer coating in the oven at about 50 oo to a dry coating weight of 37.5 9', apply the coating tape to 1/2 inch (1.27
Open a slit in the width of skin), and then insert "VHS" and "
It was loaded onto a Betamax format video cassette.

Two video cassettes, one in Betamax format and one in VHS format, at 40:00 and 80:00.
The video recorder was tested for 500 cycles at % relative humidity, at which point the test was terminated. None of the tapes broke. Recent industrial standards are 200 without fail.
Multiple passes are required. Both Betamax cassettes were tested for an additional 1000 cycles and again no failures occurred. One Betamax cassette was tested for 1500 cycles and the tape did not fail. Examples IA and IB Two Betamax video cassette tapes were prepared that were the same as those of Example 1 except with twice and half the coating weight, respectively.

Each was similarly tested at 40°C and 80% relative humidity without failure.
Passed 00 cycles. EXAMPLE IC The same ferrite telechelic polymer was coated onto the recording layer of each of several endless-loop, 8-track audio recording tapes, the recording layer comprising iron oxide particles in a non-magnetizable binder. It consisted of

Compared to typical endless-loop, 8-track audio recording tapes currently on the market, there was at least a five-fold improvement in stiffness at normal room temperature and 50% relative humidity. EXAMPLES ID and IE One lubricating coating contains 2 parts of telechelic polymer.
．． Two Betamax video cassette tubes were prepared identical to those of Example 1, except that the other contained 5 parts by weight of butyl myristate and 2 parts by weight of myristic acid.

When tested at 40oo and 80% relative humidity, the first tape passed 2000 cycles and the second 500 cycles without fail, at which point the test was stopped.

The following telechelic polyether polymers were tested as lubricants on the same magnetic recording tape as in Example 1, but the test results are shown here only for Betamax video cassettes. The fluorinated polymers of Examples 1-8 had the following values: 5s, Example 1 had the following values:
,000 Hz and at 100 Hz, with the exception of Example 8, which was measured at 1000 Hz).

Each test of the tapes of Examples 2-8 was continued until failure or no more than 500 cycles at 40oo and the indicated relative humidity.

Blockage of the tape, severe scratches on its magnetic layer, visible buildup of paint residue on the video head, loss of video signal, or sticking of the tape to the video diaphragm, audio rack, or any other surface. Each test was stopped immediately after any failure. The results are summarized below. Test results * oIPA that shows no failure after 500 to 500 cycles measured at 20℃
= Isopropyl alcohol Freon = “Freon” 11
Example of 2F of 00F200 commercially available as 3
9.0.3 mol of the telechelic polymer of Example 1, 29.
It was dissolved in CCIF2CC12F of 7 days.

While rotating the 35mm hard magnetic recording disk at 360 pm, the recording surface was wiped several times with a soft tissue impregnated with this solution.

The surface was then wiped with a dry soft tissue two minutes after the solvent had evaporated to disperse the lubricant and remove excess. The recording surface of the hard disk consisted of fine magnetizable iron oxide particles in a thermosetting epoxy resin binder. 36
With a disk rotating at 0.000 pm, a tissue soaked in inpropyl alcohol was pressed against the disk with sufficient finger pressure to move the tissue several times across the recording surface.

The fluorinated telechelic polyether polymer was resistant to such cleaning as shown by surface tension testing with n-decane. This lubricated disc passed the post-clean slide test and the post-clean slide friction test as described below. Post-cleaning slide test After cleaning with isopropyl alcohol as described above,
The disk rotates on the data standard spindle at 12 pm, but
This is the speed at which an IBM 3348-type recording head remains in contact with the recording surface. After two hours at normal room temperature, the disk and head are then inspected with the naked eye and there are burnt marks on the recording surface. A failure is indicated either when or when the head accumulates a noticeable residual liquid.

Post-Cleaning Slide Friction Test During the post-cleaning slide test, the friction between the head and recording surface is monitored periodically and continuously or intermittently at any point during the two-day period.4. A failure is indicated if a frictional force greater than 5 times is applied to the head.

If a value greater than 4.5 mm is initially observed in this test, this indicates too much lubricant coverage, in which case the coating thickness can be accepted by wiping with a dry soft tissue. reduced to a level that is

Example 10 The telechelic polymers of Examples 2, 5, and 7 and the following telechelic polymers were similarly applied to the recording surface of a hard magnetic recording disk as in Example 9, and each of these lubricated disks Passed each of the post-cleaning slide test and the post-cleaning slide friction test.

HOOC-C20÷CF2CF20)mkiCF20)n
-CF2-COO day (where m and n are loo0 to 5
each integer giving a number average molecular weight within the range of 000)
.

Example 11 Both the post-clean slide test and the post-clean slide rub test when Example 1 was repeated except that the magnetic recording disk had the binder-free recording surface of U.S. Pat. No. 3,973,072 (Anderson). I passed the exam.

Claims (1)

[Claims] 1. Magnetic recording in which the magnetizable layer has a lubricating coating made of a fluorinated telechelic polyether polymer with a background consisting of -C_aF_2_a-O- units, where a is an integer from 1 to 4. A magnetic recording medium, wherein the background is terminated with at least one polar group and the μ^2/MW of the polymer is at least 19 x 10^-^4 Debye-mol/g. 2 At least one polar end group is -CO_2R (where R is alkyl of 1 to 6 carbon atoms, 6 to 1
aryl or alquaryl of 0 carbon atoms) or ▲mathematical formula, chemical formula, table, etc.▼(wherein each R' and R'' are hydrogen, alkyl of 1 to 6 carbon atoms, benzyl, or -R'''OH ( R''' is an alkylene group of 2 to 6 carbon atoms)), -C_bH_2_bOH, -C_bH_2_bNR'R'', ▲There are mathematical formulas, chemical formulas, tables, etc.▼, or -C(OH)_2C_bF_2_b_+_1 (where b
is an integer from 1 to 4). The magnetic recording medium according to claim 1. 3. The magnetic recording medium according to claim 2, wherein the fluorinated polyether polymer is selected from the following formulas, chemical formulas, tables, etc., and m and n are each integers. 4. A magnetic recording medium according to any one of claims 1 to 3, wherein the fluorinated polymer has a Ferrantie-Schiary viscosity of at least 20 centipoise. 5. A magnetic recording medium according to any one of claims 1 to 4, wherein the fluorinated polymer has a Ferrantee-Schiary viscosity of at most 2000 centipoise. 6. The magnetic recording medium according to any one of claims 1 to 5, wherein the telechelic polymer has a number average molecular weight of at least 1,000. 7 Up to 90% by weight of the lubricating coating consists of fatty acids or esters and the coating weight is 25-150 mg/m^
2. The magnetic recording medium according to any one of claims 1 to 6.