GB1562670A

GB1562670A - Magnetic recording media

Info

Publication number: GB1562670A
Application number: GB5393277A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1976-12-31
Filing date: 1977-12-28
Publication date: 1980-03-12
Also published as: DE2756584B2; BE862471A; DE2756584C3; DE2756584A1; NL7614609A; FR2376196A1; JPS5385402A

Description

(54) MAGNETIC RECORDING MEDIA (71) We, N.V. PHILIPS' GLOEILAMPENFAB RIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a magnetic recording medium of the kind comprising a carrier having a magnetizable coating thereon which comprises a magnetic pigment dispersed in a binder with a lubricant.

The carrier is a non-magnetic material and, usually, is in the form of a tape, plate or disc which is usually manufactured from plastics materials, for example, polyester or polyvinyl chloride. The carrier may also be manufactured from nonmagnetic paper, glass or metal.

The magnetic pigment contains the usual magnetizable particles, such as, metal powder, for example Fe-powder or metal oxide particles, for example Fe2O3- particles and CrO2-particles. The particles are generally needle shaped and may have a length of approximately O.l--lpm and a thickness of approximately 0.01--0.2 Sum.

The pigment is finely distributed in the binder by means of a dispersion agent.

Dispersion agents for example, lecithin, if desired, in combination with a drying oil, mono- or diesters of phosphoric acid and alcohols, and alkylarylsulphonic acids are conventionally used for this purpose.

The binder may also be a conventional material. Examples of suitable binders are polyvinyl chloride, polyvinyl acetate, polyacrylate, polyester, polyester amide, polyurethane and copolymers of at least two monomers, which may be selected, for example, from vinyl chloride, vinyl acetate, acrylbnitrile, vinyl alcohol, vinyl butyral and vinylidene chloride.

It has been found that as a result of the continual development of recording apparatus, for example recording and playback apparatus, which are faster in use and more accurate in recording and playback more and more stringent requirements are imposed upon the quality of recording media used in the apparatus, in particular media such as, magnetic tapes. The requirements to be imposed in particular relate to the electro-acoustical properties of the media, such as, magnetic tapes, and are especially concerned with the signal strength, the signal accuracy, and also to the mechanical properties, for example, of tapes, which include properties, such as, tensile stress, resistance to wear and influence of the weather. It is important to note that it is frequently necessary to use and to store tapes for example, for relatively long periods of time and under varying ambient circumstances, for example, under a wide range of temperature differences, under a wide range of relative humidities of the air, and under various differences in exposure to U.V.-radiation by sunlight.

Also in connection with these requirements the recording medium comprises a lubricant. The following requirements or criteria may also be imposed upon a suitable lubricant. The lubricant should be able to reduce the resistance to friction which the recording medium, for example a magnetic tape, experiences on being transported along, for example, the recording and playback head. This reduces detrition of the tape. In this connection, the dynamic coefficient of friction (y) of, for example, a magnetic tape, in audio use, may have a maximum value of 0.3--0.5 and, in video use, a maximum value of 0.2#)A.

The lubricant also should be capable of preventing or at least considerably suppressing the occurrence of so-called "stick slip" and Squeal" upon transport of, for example, the magnetic tape in the recording apparatus. The expression, "Stick slip" is to be understood to mean an irregular transport of the tape in which the tape is alternately stationary and travels further. The expression, "Squeal" is to be understood to mean an irregular tape transport in which the speed of the tape is not constant but no stationary condition of the tape occurs.

The use of the lubricant may not, furthermore, result in a deterioration of both the mechanical properties of the magnetic tape, such as, loss of tensile strength, loss of elasticity, and of the electro-acoustical properties, such as, signal deterioration or signal modulation.

The above requirements or course, are necessary over the relatively long periods of storage and under the aforesaid changes in the varying climatological conditions.

Many lubricants with a variety of properties are known for use in magnetic recording media. Surprisingly, however, it has been found that the lubricants conventionally used so far, for example, oleic acid, stearic acid, silicone oil, fatty acid derivatives, such as' fatty acid esters and zinc stearate, as well as solid lubricants, such as paraffin e.g. as available under the registered Trade Mark "Vaseline"; and graphite and MoS2 do not sufficiently satisfy the above-described requirements.

For example, the use of oleic acid or stearic acid in magnetic tapes causes a significant deterioration in mechanical properties of the tape. Furthermore, the reduction of the coefficient of friction is insufficient and the tape shows a poor behaviour in the life test. The lift test is a standard test in which the tape is transported along a Sandust head at a velocity of 4.75 cm/sec. The tape stress is approximately 20 g. After 100 passages of the tape along the head the acoustical characteristic of the tape is determined, for example, the Maximum Output Level (MOL). The life test can be carried out under severe climatological conditions at a temperature of 30"C and a relative humidity of 90%.

The use of silicone oil as a lubricant in a magnetic tape also provides an insufficient reduction of the coefficient of friction but does prevent an irregular tape transport, such as "stick slip" and "squeal." In this case also a poor behaviour in the life test may occur.

The fatty acid derivatives also conventionally used as lubricants initially provide a significant reduction of the coefficient of friction but upon repeated use of the tape the coefficient of friction again increases. In this case also the behaviour in the life test is poor while in addition the tape becomes much more sensitive to moisture.

Solid lubricants, for example graphite, roughen the surface of the tape, which is detrimental to the electro-acoustical properties. In addition, the reduction of the coefficients of dynanic friction is only of a very temporary nature.

One object of the invention is to provide a magnetic recording medium and in particular a magnetic tape which has a low coefficient of dynamic friction which, surprisingly, does not increase upon repeated use of the recording medium in the recording apparatus and may even become reduced. The recording medium furthermore shows good electro-acoustical and mechanical properties in which it should be noted in particular that these properties are maintained also in adverse climatological conditions. In other words, the recording medium shows an improved behaviour in the life test. Furthermore, the recording medium shows an improved resistance to wear and, when used in the recording apparatus, has a relatively regular transport travel in which substantially no "stick-slip" or "squeal" occurs.

According to the present invention there is provided a magnetic recording medium comprising a carrier having thereon a magnetizable coating which comprises a magnetic pigment dispersed in a binder as well as a lubricant and is characterized in that the lubricant is the reaction product of a mono- or polyisocyanate with a saturated or unsaturated aliphatic alcohol, a saturated or an unsaturated aliphatic primary or secondary amine, or a saturated or an unsaturated aliphatic carboxylic acid, in which the aliphatic chain of the alcohol, amine or carboxylic acid contains from 1024 carbon atoms.

The above-mentioned reaction product has a urethane structure if the monoor polyisocyanate is reacted with alcohol; a urea structure upon reaction with a primary or secondary amine; and an amide structure upon reaction with a carboxylic acid.

The lubricant may also be obtained by reacting a specific isocyanate with the above-mentioned alcohol, amine or carboxylic acid. No limitations are placed on the isocyanate used but for most practical purposes, only those isocyanates which are non-poisonous or only slightly poisonous due to their relatively low vapour tension are used. These are commercially available, for example, as polyisocyanates for example, under the registered Trade Mark, "Desmodur".

Suitable lubricants are represented by Formulae 1 to 7 as hereinafter described and these may be obtained by a) reacting a saturated or unsaturated aliphatic mono-isocyanate with the above-mentioned alcohol, amine or carboxylic acid according to the reaction equation CmH2m1NCO + CnH2ni, X > CmH2mB NHCOYCnH2n+, +(HX) + (CO2)ss, (formula 1) in which formulae X is -OH when Y is --OO-, a is 1 and P is 0, X is -NH2 when Y is -NH-, a is 0, P is 0, X is --NH--CnH2n1 whe Y is --N(CnH2n1)--, a is 0, ss is 0, or X is -COOH when Y is a single bond between the adjacent carbon atoms, a is 0, pis 1, and m and n are equal or different and have the values 1024, or b) reacting a saturated or unsaturated aliphatic di-isocyanate with an alcohol, amine or carboxylic acid according to the reaction equation OCN-R-NCO + 2CnH2n+, X - > CnH2n1 Y-CO-NH-R-NH-CO-Y-CnH2n1 + (HX)2a + (CO2)2p (formula 2) wherein X, Y α, p and n have the aforesaid meanings and R is an alkyl group or a cyclo-alkyl group having 1--10 carbon atoms which may be substituted with alkyl, alkylene or alkyl-substituted alkylene, in which each alkyl or alkylene group comprises 1--4 carbon atoms, or c) reacting an aliphatic tri-isocyanate with an alcohol, amine or carboxylic acid according to the reaction equation

(formula 3) wherein X, Y, a, p and n have the above meanings and p = 1--10, or d) reacting an aromatic isocyanate with an alcohol, amine or carboxylic acid according to the reaction equation.

FORMULA 4 wherein X, Y, a, p and n have the aforesaid meanings, q is 2 or 3, with the proviso that when q is 2, R, is the group CaH2a, wherein a is 1--4 and, when q is 3, R, represents the groups CaH2a~" or e) according to the reaction equation

FORMULA 5 in which formulae X, Y, α, ss and n have the aforesaid meanings and R2 is an alkyl group having 1--4 C-atoms which in the phenyl ring occupies the ortho- or para position with respect to the groupNCO or the --NH--CO--Y--CnH2n1 group, and R3 is a lower alkyl group having 1--4 C-atoms.

or f) reacting a heterocyclic isocyanate with an alcohol, primary amine or secondary amine according to the equation

FORMULA 6 in which formulae X, a, 3, and n have the aforesaid meanings, R4 is a group which can be represented by the formula

wherein R, is an alkyl group having 1--4 atoms, or by the formula ACH2)rnNCO, wherein r = 1-10, and Ras is a group which may be represented by the formula

or by the formula --(CH2)r--NH--CO--Y--CnH2n1 wherein Re, r, Y and n have the aforesaid meanings. Thus the lubricants obtained by the above reactions a) to f) are represented by the formulae 1 to 6, respectively.

In particular the substances according to the above formulae 16, wherein Y is an oxygen atom, show an excellent lubricating effect. This applies in particular to the substances according to formula 3, wherein Y is an oxygen atom. The lubricating effect is promoted if the lubricant contains an excess of the alcohol reagent, so of a compound which satisfies the formula CnH2n+, OH wherein n = 10 to 24.

Mixtures of the above compounds may also be used as lubricants.

Furthermore, in lubricants which contain several --CnH2n1 groups per molecule (see formulae 26) the value of n may differ in the various groups. It will be obvious that such mixed compounds are prepared by reacting the polyisocyanate with a mixture of substances of formula CnH2n+,X, wherein the value of n differs mutually. For explanation hereof may be mentioned as an example the reaction of a polyisocyanate with a mixture of cetyl alcohol and oleyl alcohol.

Examples of readily useful specific lubricants are represented by Formulae 7-36 below.

C18H37-O-CO-NH-C18H37 (7) C16H33Z-O-CO-NH-C16H3 (8)

Compounds 16-24 especially compounds 20-22 have a relatively perfect lubricating effect and they may be used on their own or as mixtures e.g. in the form of a mixture of mixed compounds in the magnetic recording medium according to the invention. The compounds 20 and 22 are obtained by reacting the polyisocyanate of the formula

(Desmodur N) with cetyl alcohol and steary alcohol, respectively.

Compounds as represented by formulae 1 to 3 above may be used as lubricants in the magnetic recording medium according to the invention. The preparation of these compounds is carried out, as may be apparent from the above, according to methods which are known per se for the preparation of similar compounds. As may be derived from the above-stated methods of preparation a tofthe method relates to the coupling of an isocyanate (-N=C=O) group with a hydroxy group, amine group or carboxylic acid group while forming an urethane compound

a urea compound

or an amide compound

respectively.

The reaction is carried out in an inert organic solvent at a temperature which may vary from room temperature to the boiling point of the solvent used. If desired, a catalyst may be added, for example, dibutyl tin dilaurate. Suitable solvents are, for example, aromatic hydrocarbons, for example benzene and toluene, ketones such as methyl ethyl ketone, ethers such as diethyl ether and tetrahydrofuran and chlorinated hydrocarbons such as chloroform.

The preparation of the recording medium according to the invention may be carried out in the usual manner, for example, by thoroughly mixing the magnetizable particles, the dispersing agent and a part of the binder in a solvent for the binder by means of a ball mill. The remainder of the binder dissolved in a suitable solvent and the lubricant are then added and the whole is ground for another few hours in the ball mill. As solvents for the binder may be used organic liquids, for example, esters, for example ethyl acetate, ethers, for example tetrahydrofuran, ketones, such as methyl isobutyl ketone, cyclohexanone, chlorinated hydrocarbons, such as 1,2-dichloroethane. It is also possible to perform the above-mentioned process in one step in which all the ingredients are supplied simultaneously to the ball mill. The quantity of lubricant is not restricted to narrow limits and as a rule is from 1 to 10% by weight calculated on the quantity of binder.

After thoroughly grinding the dispersionin the ball mill, the larger magnetizable particles which may still be present are sieved out and the resulting magnetizable coating is provided on the carrier in a uniform layer.

As already stated above, the carrier may be in the form of a tape, plate or disc and the like and, dependent on the material from which the carrier is manufactured, may be provided, if desired, with a suitable adhesive layer for the magnetizable coating to be provided on the carrier. In addition to the adhesive layer, other layers such as an antistatic layer, may be provided. The whole is then dried, the solvent evaporated, and a recording layer remaining on the carrier in a thickness of 2 to lOU.

If desired, this layer may be hardened so as to increase the resistance to detrition and may moreover be subjected to a calendering process in which the surface of the layer becomes smoother.

By way of illustration certain embodiments of the invention will now be described in more detail with reference to the following specific examples.

Examples: la. Preparation of lubricant which contains a mixture of compounds as well as a mixed compound which satisfies the formula

wherein n = 16 and 18.

451 of acetone, 9 kg of a mixture (1:1) of cetyl alcohol and stearyl alcohol and 3kg of dibutyl tin dilaurate (catalyst) are mixed while stirring continuously in a 1001 stainless steel vessel having a stirrer. The whole was heated to the boiling point after which a solution of 7.05 kg of a polyisocyanate of the formula (Desmodur N of the accompanying drawings).

(trade name (Desmodur N)) in 16.2 1 of acetone were added. The whole was refluxed for 3.5 hours (560C). After cooling, the crystallizate was filtered off and washed with acetone (36 1). After evaporating the solvent 13.5 kg of the abovementioned product were obtained. The other substances indicated above by formulae 7-36 were prepared in an analogous manner.

Ib. Preparation recording medium.

In a ball mill having balls of 6--9 mm diameter, 100 g of rFe203 (magn.

pigment) were mixed with 4 g of lecithine, 230 g of a 12.5% solution of polyurethane resin (Trade name Estane) in tetrahydrofuran, as well as 1.4 g of lubricant obtained according to example 1. The mixture was ground in the ball mill for 48 hours to a fineness < 2,um. The product was drained, filtered through a cellulose-asbestos filter and provided on a 1 2y thick carrier foil of polyethylene terephthalate. The assembly of carrier and provided magnetizable coating was dried and calendered in which ultimately a layer thickness of the magnetizable coating of 6N was obtained.

In the same manner, recording media which contained the lubricants stated in column 1 of the following table were prepared. The recording media differ mutually only in the nature of the lubricant used, so that the recording medium is fully characterized by the state of the lubricant used. The melting point of the lubricant is recorded in column 2. A few important characteristics of the recording medium strongly influenced by the lubricant are recorded in columns 3, 4 and 5.

Column 3, for example, states the difference in coefficient of dynamic friction of the recording medium measured after 100 passages of the medium along a steel pin having a roughness of Ro = 0.08 ,um (90 reversal angle and tape speed of 500 mm per minute) and measured after I passage of the medium (tape) along the steel pin.

Column 4 states the coefficient of friction of the medium after 50 passages of the medium along the pin.

In column 5 is recorded the behaviour in the life test of the recording medium under severe climatological conditions. The life test has already been described above. It relates to the signal loss after 100 passages of the tape along a Sandust head at 300C and a relative humidity of 90%. The signal loss is determined by measurement of the maximum output level (MOL) at 3% distortion and 3100 Hz.

The result is indicated by "+", "~" and "-", where + = signal loss smaller than 2 dB + = signal loss of 2-5 dB - - signal loss exceeding 5 dB.

For comparison, the table also states the data of recording media in which the known lubricants stearic acid, oleic acid and silicone oil have been used.

Lubricant Reaction product of a b m.p. C 100- 1 50 life test CloH2lNH2 *Desmodur N 99 0.1 0.50 C16H33NH2 Desmodur N 116 -0.1 0.43 + Cl,,H3,0H Desmodur N 67 -0.2 0.20 + Cl6H33OH Desmodur N 63 -0.2 0.28 + C22H45OH Desmodur N 85 -0.3 0.21 + Cl8H37NH2 Desmodur N 118 -0.2 0.25 + Cl8H35OH Desmodur N 120 -0.1 0.42 + C18H3,OH isophorone- 64 -02 0.30 + di-i socyanate C22H45OH **Desmodur L 74 -0.1 0.28 + Cl8H37OH Desmodur L 68 -0.1 0.40 stearic acid +0.4 0.85 oleic acid jams > 2 silicone oil 0.60 * Desmodur N is a polyisocyanate of the formula.

** Desmodur L is a polyisocyanate of the formula

Claims

WHAT WE CLAIM IS: - l. A magnetic recording medium comprising a carrier having thereon a magnetizable coating which comprises a magnetic pigment dispersed in a binder with a lubricant, characterized in that the lubricant is the reaction product of a mono- or polyisocyanate with a saturated or unsaturated aliphatic alcohol; a saturated or unsaturated, aliphatic primary or secondary amine; or a saturated or unsaturated aliphatic carboxylic acid, in which the aliphatic chain of the alcohol, amine or carboxylic acid contains from 10 to 24 carbon atoms.
2. A magnetic recording medium as claimed in Claim l, characterized in that the lubricant is (a) a compound represented by formula l as hereinbefore described.

in which formula Y is an oxygen atom, a -NH-group, a N(CnH2nj) - group or a single bond between the adjacent carbon atoms and wherein n = l024 and m = 10--24 (b) is a compound represented by formula 2 as hereinbefore described.

in which formula Y and n have the aforesaid meanings R is an alkyl group or cyclo alkyl group having 1--10 carbon atoms which may be substituted with alkyl, alkylene or alkyl-substituted alkylene, in which each alkyl or alkylene group contains 1--4 carbon atoms, (c) is a compound represented by formula 3 as hereinbefore described in which formula Y and n have the aforesaid meanings and p = 1--10, (d) is a compound represented by formula 4 as hereinbefore described in which formula Y and n have the aforesaid meanings q is 2 or 3, with the proviso that when q is 2, R, represents the group CH2a, wherein a is 1--4, and when q is 3, R, represents the group C,H2a~" e) is a compound represented by formula 5 as hereinbefore described in which formula Y and n have the aforesaid meanings, R2 is an alkyl group having 1--4 C atoms which in the phenyl ring occupies the ortho- or para-position with respect to the group --NHH-CO-Y-CnH2n1 and R3 is a lower alkyl group having 14 C atoms, (f) is a compound represented by formula 6 as hereinbefore described in which formula R5 is a group which is represented by the formula

or by the formula HCH2),NHCOYCnH2n, in which formula Y and n have the aforesaid meanings, R6 is an alkyl group having 1--4 carbon atoms, and r = 1-I 0.
3. A magnetic recording medium as claimed in Claim 2, characterized in that the lubricant is a compound which satisfies the formula

wherein n = 10--24 and p = 1-1 0.
4. A magnetic recording medium as claimed in Claim 2, characterized in that the lubricant is a compound which satisfies the formula 20 hereinbefore described.
5. A magnetic recording medium as claimed in Claim 2, characterized in that the lubricant is a compound which satisfies the formula 22 hereinbefore described.
6. A magnetic recording medium as claimed in Claim 2, characterized in that the lubricant is a compound which satisfies the formulae hereinbefore described.
7. A magnetic recording medium as claimed in any of the preceding Claims, characterized in that the lubricant also comprises a compound of the formula CnH2n*1OH, where n = 1W24.
8. A magnetic recording medium which contains a compound or a lubricant as renreqented hv anv of clams I to 7
9. A method of preparing the magnetic recording medium claimed in claim l substantially as hereinbefore described.