CA1139158A - Flexible magnetic recording media lubricated with fluorinated telechelic polyether polymer - Google Patents

Abstract

FN 915,539 Abstract of the Disclosure Flexible magnetic recording tape is lubricated by a thin coating of a fluorinated telechelic polyether polymer having at least one polar groups such as -CONHCH2CH2OH , -COOCH3 , -CH2OH , and -COCF3 . This is believed to provide for the first time reliably effective lubrication at 40°C and 80% relative humidity.

Description

~ 3~ FN 915,539 -L-YLEXIBLE MAGNETIC RECOR~ING MEDIA LUBRICATED WITH
FLUORINATED TELECHELIC POLYETHER POLYMER

The invention concerns the lubrication of flexible magnetic recording medla such as tapes and cards.
It has been known since the advent of magnetic recording media that their recording surfaces should be lubricated to permit sliding contact with recording heads and to inhibit adjacent convolutions o wound tape from sticking to each other after prolonged storage. The first lubricants were atty acids and esters such as carnauba wax. These were either added to the dispersion of the magneti2able particles and binder resin or coated over the finished r~cording surface. The fatty acid and ester lubricants were considered to be satis~actory at ordinary ambient conditions but were not reliable at high tempera-tures and relative humidity, e.g., 40C and 80~ relative humidity.
U.S. Patent No. 3,490,946 suggests the use of 1uorocarbon compounds as lubricants for flexible magnetic recording tapes, either applied as a surface layer or dispersed into the mixture of binder and magnetizable particles. U,S. Patent No. 3,778,308 more specifically suggests perfluoroalkyl polyethers a3 lubricant coatings for magnetic recording media. U.S. Patent No. 3,95~,637 prepares a surface lubricant for magnetic recording tape from a dispersion in trifluorotrichloroethane of ~a) a copolymer of trifluoroethylene and vinyl chloride and (b) .r3~

2--a telomer of tetrafluoroethylene. This is then filtered to remove undissolved polymeric solids to provide a solution Erom which the lubricant is applied.
O~ current flexible magnetic recording media, about 70 percent have fatty acid and ester lubrication and most of the others employ silicone lubrication. While it is believed that no magnetic recording tape now on the market e~ploys a fluorinated lubricant, one manufacturer uses such a lubricant for the flexible magnetic recording disk of a diskette oE the type shown ln U.S~ Patent No~

3,668,658.
The present invention concerns a magnetic recording medlumcomprising a flexible backing and a magnetizable layer which has a lubricating coating that reliably provides effective lubrication at 40C and 80 relative humidity. Surprisingly great latitude in the weight or thickness of the lubricating coating can be tolerated without interfering with that novel achievement.
That lubricating coating comprises a fluorinated tele-2a chelic polyether polvmer having a backbone comprising-CaF2a-O- units wherein a is an integer from l to 4, which backbone is terminated by at least one polar group such that ~2/MW is at least l9 x 10-4 Debye2-moles/g.
"Telechelic" polymers have low molecular weight and known fùnctional terminal groups.
The dipole moment ~ of the fluorinated tele-chelic polymer can be calculated from the Onsager Relation -.~L~3.f~

11 2 , 9 k_T MW ( s -~ ( 2

4~ No d ES (~+2)2 where k = Boltzmannls Constant T = Temperature in K
MW = Molecular Weight No = Avogadro's Number d = Density ES = Dielectric constant measured at low frequencies, 0 E~ = Dielectric constant measured at high frequencies, whera the approximation is made through Maxwell's Relations that ecO = nD2 ~(5-lo~nD2~l~o7s nD2 where nD is the refractive index of the material at the sodium D line at 20C.
The fluorinated telechelic polyether polymer pre~erably has a number average molecular weight of at least 1000 and a Ferranti-Shirley viscosity (measured at 1640 sec 1 and 20C.) of at least 20 centipoise. The number average molecular weight of fluorinated telechelic polyether polymers having more than one terminal polar group per polymer molecule is preferably somewhat higher ; as compared to telechelic polymers having only one terminal polar group. For examp e, where there are two terminal polar groups per polymer moleculs, the number average molecular weight preferably exceeds 1500.

.
' ' Useful polar groups :Eor tho Eluorinated telechelic polyethers include -C02R wherei~ is alkyl of 1 to 6 carbon atoms, aryl or alkaryl o:E 6 to 10 carbon atoms; -~`NI~ " wherein each o:E R ~and ~" is hyclrogen, alkyl of 1 to 6 carbon atoms, benzyl, or -R'l'01-1 where R"' is an alkylene group oi 2 to 6 carbon 0 bl2bll; Cbll2bNI~ ler~in R ~Incl Ic"

-eCbF2b~l; or -C(011)2CbF2b~l wherein b is an integer of 1 to 4. Strongly acidic polar groups such as carboxylic or sulfonic acid groups are less desirable because they are potentially corrosive. ~is may be minimized by conversion to salts. Preferably the pKa of the telechelic polyether polymer is at least 1Ø
Preferred fluorinated telechelic polymers have the backbone -[CF2C~20¦ -[C120~1 -, wllere m is an integer :trom about 6 to 32 and n :is an integer erom about 12 to 52, as disclosed in Unitcd Statcs Patentx 3,810,87~1 and 4,085,137, or the backbone ECI;tC1-3~CF20~n or ECl2cl~cE3)o3nJ where n is an integcr :Erom about 6 to 20J as clisclosecl:in United States ~-5 Patents 3~250/808 and 3,699,145O
Such fluorinated telechelic polyethers are readily produced to have number average molecular weights within the preferred range of 1000-5000 and Ferranti-Shirley viscosities (measured at 1640-1 sec) withln th~
preferred range of 20-2000 centipoise. The fluorinated telechelic polyether polymer may also contain -CF2-CF2-units which increase the separation between the ether oxygens and tend to make it necessary to avoid number average molecular weights toward the high end of the preferred range of 1000-5000 mentioned above. Otherwise, the viscosity of the fluorinated telechelic polyether polymer might be too high to provide good lubrication.
Superior lubrication has been attained by applying the fluorinated telechelic polyether polymer with a rotogravure coater from solutions or emulsions as dilute as 0.1~ by weight, thus producing what is believed to be a coating weight of about 10 mg/m2. Such a COatincJ is approximately of monomolecular thickness. There has been no testing to assure that a coating of that thickness could continue to provide effective lubrication for a period of years. The actual coating weights are so small as to be difficult to measure, but superior lubrication has been achieved at coating weights which are believed to be about 10 to 150 mg/m2. It is currently preferred to apply the fluorlnated telechelic polymer from a 0.4-0.8%
solution or emulsion to provide coating weights of about ~ 1 A ~

25-60 mg/m~. This should provide reasonable assurance of good lubricating properties under adverse environmental conditions for a number of years.
It may be desirable to blend the fluorinated telechelic polyether polymer wlth other lubricants such as fatty acids and esters to provide reliable stop-motion in video tape recorders at high temperatures and high relative humidity. The fluorinated telechelic polyether polymer should comprise at least 10~ by weight of the blended lubricants. Preferably the coating weight o the blended lubricants is from 25 to 150 mg/m2.
The backing member of each of the magnetic recording media of the ollowing examples was a flexlble biaxially-oriented polyethylene terephthalate film having a thickness of approximately 15 micrometsrs.

Example 1 A preferred 1uorinated telechelic polyether polymer of the invention is O O
~ H~tcH2~2N~c-cF~otcF2cF2o)m~cF2o)n-cF2-c-NH~cH2t2oH , where C2 ~b~ e m and n are each integers providing ~R_.~o~ag~ molecular weight of about 2000, and has a Ferrantl-Shirley viscosity of 1440 cps. 0.3g of this telechelic polyether was emulsified in 60g of isopropyl alcohol, and the emulsion was applied with a rotogravure coater over the recording layer of a flexible magnetizable recording tape. The recording layer comprised fine acicular magnetizable iron ~3~

oxide particles in a binder comprising crosslinked poly-vinyl chloride copolymer and polyester polyurethane. The recording layer was specifically designed for helical-scan video recording except that it contained no lubricant.
Ater the telechelic polymer cvatlng was dried in an oven at about 50C to a dried COatinCJ weight of about 37,5 mg/m2~ the coated tape was slit to one-half-inch (1.27-cm) widths and then loaded into videocasset~es of the "V~S" and l'Betamax" formats. Two videocassettes of the Betamax format and one of the VHS format were tested on videorecorders at 40C and 80~ relative humidity through 500 cycles, at which point the tests were terminated, None of the tapes had failed. Current indu~try stanclards re~uire 200 passes withou~ ~ailure.
~oth of the Betamax cassettes were further tested to 1000 cycles, again with no failures. One Betamax cassette was tested to 1500 cycles, and its tape did not fail.

Examples lA and lB
Two Betamax videocassette tapes were prepared which were identical to those of Example 1 excspt having twice and half the coating weight, respectively. E'ach also passed 500 cycles at 40C and 80% relative humidity without failure.

Example lC

The same fluorinated telechelic polymer was coated over the recording layer of each of several endless-loop, 8-track audio recordiily tapes, the recording layers of which comprised acicular iron oxide partlcles in nonmagnetizable binder. At least 5-fold impcovement was noted in resistance to wear at ordinary room temperature and 50% relative humidity as compared to typical endless-1OOPJ 8-track audio recording tapes now on the market.

Examples lD and lE
, Two Betamax videocassette tapes were prepared which were identical to those of Example l except that one lubricating coating contained 2~5 parts by weLght of butyl myristate and the other, 2 parts by weight of myristic acid per part of the telechelic polymer~ When tested at 4nC and ~0% relative humidity, the ~irst tape passed 200 cycles and the second passed 500 cycles without ~ailure, whereupon testing was discontinued.
The following telechelic fluorinated polyether polymers were tested as lubricants for the same magnetic recording tape as in Example l except that the test results are here reported only for Betamax videocassettes.

r3~

g Viscosi ty Example No.ave. (Fer-Sh) No ~ . MWCps .
l 2 CH3C~CF2~CF2CF2)m~CF2)n 2 3 2 2o~cF2CF20)m~CF20)n~CF2~CEi20H 2000 24 4 ditto 4000194 FF3 l CF3-0~CF2-CF-O)nCF~-C-CF3 2600 125 fF3 fF3 6 F(CF-CF2-O)n~CF-COOH 32001130 7 F(CF-CF2-O)n-CF-C02CH3 3200 345 fF3 1CF3 1l 8 F(CF-CF20~n-CF ~ C-NH(CH2)20H 3300 1785 Comparative Example No.
CF
A CF3-0-(CF2CF-O)n-CF2CF~CF3 3600 708 CF
B F(CF CF2 )n C2F5 1300 77 The fluorinated polymers oE Example 1-8 had the following values (~s being measured at 100 Hz, except Example 1 at ltO Hz and Example 8 at 1000 H~):

Example m n d~s ~ x104 1 8 14 1.77223~0 1~76 809 2 16 28 1.7502.8~ 05 53.7 3 8 14 1O793~.80 :l.809 ~9.4 4 1~ 28 1.814~.5S 1~805 37~
-- 15 1~8742.22 1O814 20.6 6 -- 18 1.802.361.~25 27.6 7 -- 18 1.8~82.79 1.822 46.6 8 -- 18 1.903.~81.8~3 80.2 ~ ~- 20 1.8862.14 1.816 16.7 B -- 10 1.8602.15 1.797 18.

Each test of a tape of Examples 2-8 ~nd Comparatlve Examples A and B was continued until Eailure or 500 cycles without ~ailure at 40C and the indicated relative humldity. Each test was discontinued immediately after any failure such as jamming of the tape, visual scoring of its magnetiæable layer, accumulations of visible residue on the video heads, a 6 dB loss in video signal, or sticking of the tape to the video capstan, : 20 audio stack or to any other surface. Results-are summarized below:

t~

Tast Results Polymer Relative No. of Example Concentration Vehicle Humidity Passes 2 1% IPA 85~500 0.5~ do do452 3 1~ do 80%500+ (2 tapes) 0.25% Freon do500+
4 1% ~ IPA 85%119 do do do30 do do do500+
do Freon 80~S00~ (2 tapes) do IPA do . do (2 tapes) 0.5~ do do71 6 do do do500 7 1% do dodo 0.5% do dodo 8 1% do do500+
do do do40 0.5% do do 5 do do do481 A 1% do do124 do do 85%15 0.5% do do29 B 1% do 50%* 383 0.5% do do*212 ~. ~

3~

*tested at 20C
500+ indiaates no failure at 500 cycles IPA ~ isopropyl alcohol ; E~ Freon = CClF2CC12F sold as ~reonU 113 :~ ~ r~ M~

~: :

~:: i : ~ : `, :

'~ :~ ' ' `

: , .

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Magnetic recording medium comprising a flexible backing and magnetiz-able layer, the layer having a lubricating coating comprising a fluorinated telechelic polyether polymer having a backbone comprising -CaF2a-O- units wherein a is an integer from 1 to 4, which backbone is terminated by at least one polar group, the µ2/MW of the polymer being at least 19 x 10-4 Debye2-moles/g, which lubricating coating reliably provides effective lubrication at 40°C and 80% relative humidity.

2. Magnetic recording medium as defined in claim 1, wherein at least one polar end group is selected from -CO2R wherein R is alkyl of 1 to 6 carbon atoms, aryl or alkaryl of 6 to 10 carbon atoms, or -?NR'R" wherein each of R' and R" is hydrogen, alkyl of 1 to 6 carbon atoms, benzyl, or -R'''OH where R''' is an alkylene group of 2 to 6 carbon atoms;
-CbH2bOH;
-CbH2bNR'R" wherein R' and R" are as defined above;
-?CbF2b+1;
-C(OH)2CbF2b+1 wherein b is an integer of 1 to 4.

3. Magnetic recording medium as defined in claim 2, wherein said fluor-inated polyether polymer is selected from HO?CH2?2NH?-CF2O?CF2CF2O)m?CF2O)n-CF2-?-NH?CH2?OH

CH3O?-CF2O?CF2CF2O)m?CF2O)n-CF2-?OCH3 HO-CH2-CF2O?CF2CF2O)m?CF2O)n-CF2-CH2-OH
and m and n are each integers.

4. Magnetic recording medium as defined in claim 3 wherein the fluorin-ated polyether polymer has a number average molecular weight in the range 1000-5000.

5. Magnetic recording medium as defined in claim 1, wherein the Ferranti-Shirly viscosity of said telechelic polymer is at least 20 centipoise.

6. Magnetic recording medium as defined in claim 5, wherein the Ferranti-Shirley viscosity of said telechelic polymer is at most 2000 centipoise.

7. Magnetic recording medium as defined in claim 1, wherein said tele-chelic polymer has a number average molecular weight of at least 1000.

8. Magnetic recording medium as defined in claim 1, wherein up to 90%
by weight of said lubricating coating comprises a fatty acid or ester and the coating weight is 25-150 mg/m2.