IT8047528A1 - IMPROVEMENT IN MEDIA FOR MAGNETIC RECORDINGS, SUCH AS LUBRICATED TAPES, CARDS AND DISCS. - Google Patents

Description

DESCRIPTION

accompanying a patent application for an invention entitled;

"Improvement in magnetic recording media such as tapes, cards and discs, lubricated"

SUMMARY

- Object of the invention? a magnetic recording medium whose magnetizable layer has a lubricating coating comprising a fluorinated polyether polymer having a backbone comprising units. -C F2a-0- in which a represents an integer from 1 to 4, the backbone is closed by at least one polar group and the / MW of the polymer? of at least 19 x 10-4 Debye 2 mol / gram.

DESCRIPTION OF THE INVENTION

The invention relates to the lubrication of magnetic recording media such as tapes, cards and discs

It has been known since the advent of magnetic recording media that their recording surfaces must be lubricated to allow sliding contact with the recording heads. The first lubricants were fatty acids and esters such as carnauba wax. These were either added to the magnetizable particle dispersion for binder resin as well as applied as a coating, on the finished recording surface, Fatty acid and ester based lubricants were considered satisfactory under ordinary ambient conditions but do not give reliance on high temperatures and high humidity. ? relative for example to 40? C and to a humidity? relative to 80%.

Of the current, flexible magnetic recording media, about 70% have fatty acid and ester based lubrication and most other media employ silicone lubrication. Despite the? US patents no

3-490.946 and no. 3,778,308 suggest the use of fluorine compounds as lubricants for magnetic recording media eg? they are rarely used as lubricants for flexible, magnetic recording media. On the other hand, rigid magnetic recording discs are almost always lubricated with fluorocarbon compounds such as highly fluorinated polyethers which have a scaffold comprising units? CaF2-O- in which a? .an integer from .1 to 4, for example,

in which n? an integer that gives a viscosity? of Ferranti-Shirley (hereinafter measured h -1640 sec -1) of about 75-1 350 centipoise. Such polymers are marketed by E.I. DuPont de Nemours & Co, such as oils. fluorinated "Xrytox" 143. A favorite of this group? was the "Krytox" 143 AD which has a stickiness? Ferranti-Shirley of 1322 centipoise and has a viscosity index? (ASTM D2270) of 145 and an average number molecular weight of about 7000. When these fluorinated polymers are used to lubricate the hard drives they tend to be eliminated if the discs are cleaned with icopreric alcohol.

The present invention relates to a magnetic recording medium, a magnetizable layer of which has a lubricating coating which reliably provides effective lubrication - at 40 ° C and humidity. relative of 80%. When used to lubricate hard drives, the lubricating coating resists removal when wiped with a cloth containing isopropyl alcohol.

The lubricating coating of the invention comprises a fluorinated telechelic polyether polymer which has a scaffold comprising units. CF2a-O-where at? an integer from 1 to 4 as a scaffold terminates by at least one hypolar group such that u / MW is at least 19 x 10 Debye-moles / g. The "telechelic" hypolymers have a low molecular weight and have known terminal functional groups.

the dipolar moment, U of the fluorinated teleehelic polymer pu? be calculated based on the Onsager relation

in. which nD? the refractive index of the material corresponding to the sodium hnea D at 20 ° C.

The fluorinated telechelic polyether polymer preferably has a number average molecular weight of at least 1000 and a viscosity. of Ferranti-Sirley (determined at 1640 sec-1e at 20 ° C) equal to at least 20 .centipoise. The numerical average molecular weight of the fluorinated polyester-telechelic polymers which have pi? of a polar terminal group per polymer molecule preferably somewhat higher compared to telechelic polymers which have only one terminal polar group. For example, when there are two terminal polar groups per polymer molecule, the number average molecular weight is preferred. billy exceeds the value of 1500.

Polar groups useful for fluorinated telechelic polyethers include:

CO2R where R? an alkyl group having 1 to 6 carbon atoms, aryl, or alkaryl of 6-10 carbon atoms;

-CNRT R "where each of the Rf and R"? hydrogen, alkyl of 1-6 carbon atoms, benzyl or -R "'OH where RH I is an alkylene group of two six carbon atoms;

; in which b? an integer from 1 to 4. Strongly acidic polar groups such as carboxylic or sulfonic acid groups are less desirable

since? they are potentially corrosive. There? can to be

rendered minimal by conversion into salts. Preferably the pKa of the telechelic polyether polymer

? at least 1.0.

Preferred fluorinated telechelic polymers.

have the scaffolding in which

m? an integer ranging from 6; to 32 and n? an integer from 12 to 52, as described in U.S. Pat. Nos. 3 * 810.874 and 4.085.137, or an impaicalur in which n

? an integer ranging from 6 to 20 as described

in the US breretti no. 3250.808 and no. 3.699145

Such fluorinated telechelic polyethers are readily produced to have molecule weights

average numerical re within the preferred range of 1000

at 5000 and viscosity? by Ferranti-Shirley (determined

at 1640 sec "-1) within the preferred range of 20-2000 centipoise. The fluorinated telechelic polyether polymer -can also contain -CF -CF units - to increase the separation between ether oxygens and tend to make

. -re necessary l? avoid average numerical molecular weights

_ towards the upper limit of the preferred range

-1000-5000 above mentioned. Otherwise, the. Viscosity? of the fluorinated telechelic polyether polymer pu? be too high to provide good lubrication.

Superior lubrication of the flexible magnetic recording media? was obtained by applying the fluorinated thechelic polyether polymer with a gravure coating machine from solutions or emulsions having a dilution such as to reach a concentration of 0.1% by weight, thus producing such a solution. that ? believed to be a pan coating weight at around 10mg / ra. This coating is approximately monolecular in thickness. The actual cladding weights are like this. small, yes

- they can determine with difficulty, but? superior lubrication has been obtained in correspondence of coating weights which are believed to be about 10-150 mg / m. It is currently preferred to apply the fluorinated telechelic polymer from a 0.4-0.8% solution or emulsion for provide coating weights of approximately 25-60 mg / m2. There? provides a guarantee. reasonable of good lubrication in adverse environmental conditions for a number of years.

The fluorinated telechelic polyether polymers. can be applied to discs of. rigid magnetic recording from dilute solutions or dispersions by rubbing or by any other technique such as spraying or injection. After drying, the surface should be buffed with a dry soft cloth to distribute the lubricant and to remove any excess. polishing changes the appearance from slightly dull to shiny. If a drop of 5 microliters of n-decane after 10 seconds has a diameter of about 3 mm. indicates that? was applied a continuous coating in the absence of any lubricant, the diameter of the drop can? reach 30-12 mm.

Since? Not ? known how much lubricant is removed by polishing and since? the coatings are thin,? It is difficult to determine the gold thickness. Given that a monomolecular layer of fluorinated telechelic polyether polymer is believed to be of the order of 40 Angstroms in thickness, it is assumed. that the coating is at least of that thickness. Electron scattering terminations suggest that 75-250 Angstrom thicknesses provide the preferred results. It is believed that a coating ind? Bit thickly gives? a fluorinated telechemical polymer on the hard recording disk can. cause undue resistance. advancement.

Pu? It may be preferable to mix the fluorinated telechelic polyether polymer with other lubricants such as fatty acids and esters for purposes such as to provide reliable rest-motion in high temperature and high humidity video tape recorders. relative; The fluorinated telechelic polymer must comprise at least 10% by weight of the lubricants in the mixture. Preferably, the coating weight of the blended lubricants? of 25-150 mg / m2.

The support member of each of the magnetic recording means of examples 1-8? consisting of a biaxially oriented, flexible polyethylene terephthalate film which has a thickness of about 15 micrometers.

EXAMPLE 1

-A preferred fluorinated telechelic polyether polymer of the invention?

where m and n are each an integer giving an average molecular weight of about 2000. which polymer has a viscosity? of Ferranti-Shirley of 1440 cps. 0.3 g of this telechelic polyether is emulsified in 60 g of iso alcohol.

propyl, and the emulsion is applied with a gravure applicator onto the recording layer of a flexible, magnetized recording tape. The recording layer comprises magnetizable, needle-like iron oxide particles. A binder comprising cross-linked polyvinyl chloride copolymer and polyester polyurethane. The recording tape? specifically designed for. helical scan video recording except that it does not contain any lubricant.

After the telechelic polymer coating? been dried in an oven at about 50 ° C. to form a dry coating weight of approximately 37.5 mg / m2, the coated tape is split into half inch (1.27 cm) widths and then loaded into "VHS" and Betamax "format videotapes.

Two video cassettes of the Betamax format and one of the VHS format are examined on video recorders at 40? C and at a humidity of? relative of 80%, through 500 cycles after which? the tests are finished. None of the tapes fail the test. Current industrial standards require 200 passes without failure. Both Betamax cassettes are further tested up to 1000 cycles, still without any failures. A cassette. Betamax is examined, up to 1500 cycles and its belt does not show any damage.

EXAMPLES 1A and 1B

Two Betamax videotape tapes are prepared so that they are identical to those of Example 1 except that they respectively have a coating weight which? double and half ?. Each of the belts also exceeds the pr? Va to 500 cycles at 40? C and a relative humidity of 80% without failure.

EXAMPLE 1C

The same fluorinated telechelic polymer is applied as a coating on the Recording layer of each of several continuous-circuit 8-track audio recording tapes, the recording layers of which comprise needle-like iron oxide particles in a non-magnetizable binder. An improvement equal to at least 5 times is noted as regards the resistance to wear at ordinary ambient temperature and humidity. relative to $ 50 compared to typical 8-track continuous-circuit audio recording tapes currently on the market.

EXAMPLE 1D and 1.E

Two tapes, for Betamax video cassette are prepared to be. identical to qielli.

of Example 1, except that one lubricating coating contains 2.5 parts by weight of butyl myristate and the other contains 2 parts by weight of myristic acid per part of telechelic polymer. When is the examination carried out at 40? C and at a humidity? relative by 80%, the first belt passes the test of 200 cycles and the second belt passes the test of 500 cycles without failure, after which the test is stopped.

The following telechelic polyether-fluorinated polymers are examined as lubricants for the same magnetic recording tape in Example 1 except that the test results are reported herein for Betamax video cassettes only.

Do the fluorinated polymers of Examples 1-8 have? following values (being determined at 100 Hz, with the exception of example 1, where it is determined at 10,000 Hz and example 8, where it is determined at 1,000 Hz):

Each test of a tape of Examples 2-8 is continued until failure or 500 cycles without failure at 40 ° C, and humidity. relative in? di cata. Each test is stopped immediately after any failure such as tape jamming, visually detectable fall of its magnetizable layer, accumulation of visible residue on the video heads, a loss of 6 dB in the signal video or gluing the tape on the video winch, on the audio unit or on any other surface.

The results are summarized below:

EXAMPLE 9

0.3 g of the telechelic polymer of the example are dissolved in 19.7 g of CCLF2CCl2F. While a 35 hard magnetic recording disk was being spun at 36 ?? revolutions per minute, a soft tissue saturated with the solution is rubbed across its recording surface many times. Then after two minutes during which the solvent volatilizes, the surface is polished with a dry soft cloth to distribute the lubricant and to remove any excess. The recording surface of the hard disk makes magnetizable needle-like iron oxide particles in a thermoset epoxy resin binder.

With the disc spinning at 3600 revolutions per minute, an isopropyl alcohol impregnated fabric is pressed under fingertip pressure against the disc for approximately 30 seconds while moving the fabric across the recording surface many times. fluorinated telechelic polyether polymer? resistant to such cleaning as indicated by the surface tension tests with the use of normal decane.

The lubricated disc passes each sliding test after cleaning and the sliding friction test after cleaning as described below:

. Creep test after cleaning Q? Po cleaning with isopropyl alcohol? as previously indicated, the disc is rotated at 120 rpm on a spindle for data module at a speed? at which the IBM 3348 type recording head remains in contact with the recording surface. After 24 hours at ordinary room temperature, the disc and head are then examined with the naked eye, and failure occurs if there is a bluing mark on the recording surface or if the head has accumulated a visible residue.

Sliding friction test after cleaning

During the creep test after cleaning, the friction between the head and the recording surface? checked periodically and failure occurs if a friction force greater than 4.5 grams is applied against the print head continuously or intermittently at any time during a 24 hour period

.Self. in this test we initially observe a. value greater than 4, 5 grams there? can indicate that the lubricant coating? too heavy

or dense, in which case, the thickness of the coating pu? be reduced to an acceptable level by polishing with a dry soft cloth.

EXAMPLE 10

The telechelic polymers of Examples 2, -5 and 7 and the following telechelic polymers are similarly applied to the recording surfaces of rigid magnetic recording discs as in Example 9, and each of these lubricated discs passes each slip test afterwards. cleaning and sliding friction test after cleaning:

where m and n are each integer which gives an average number molecular weight in the range from 1000 to 5000.

EXAMPLE 11

When repeating example 1, except

Claims (7)

1. Magnetic recording medium, the magnetizable layer of which has a lubricating coating comprising a fluorinated polyether polymer which has a scaffold comprising units? CaF2a-O- in which a? an integer ranging from 1 to 4, which means? characterized in that the scaffold ends with at least one polar group, the value of u2 / molecular weight of the polymer being equal to at least 19 x 10-4 Debye2-mol / g. 2 Magnetic recording medium according to claim 1, further characterized in that said means has at least one polar end group selected from -CO2R where R? alkyls of 1-6 carbon atoms, aryl or alkaryl of 6-10 caronium atoms, or 3. Magnetic recording medium according to claim 2, further characterized in that said fluorinated polyether polymer? chosen by: Magnetic recording method according to any of the previous revisions further characterized by the fact that the viscosity? of Ferranti-Shirley of said fluorinated polymer? equal to at least 20centipoise. 5. Magnetic recording medium according to any one of the preceding claims further characterized in that the viscosity? of Ferranti-Shirley of said fluorinated polymer? at the most equal to 2000 centipoise. 6. Magnetic recording medium according to any of the preceding claims further characterized in that said telechelic polymer has an average number molecular weight of at least 1000. 7. Magnetic recording means according to any one of the preceding claims further characterized in that up to. 90% in. weight of said lubricating coating? consisting of a fatty acid or ester and the weight of the coating? of 25-150 mg / m2