CA1076895A - Magnetic recording medium having segmented copolyester binder - Google Patents
Magnetic recording medium having segmented copolyester binderInfo
- Publication number
- CA1076895A CA1076895A CA254,881A CA254881A CA1076895A CA 1076895 A CA1076895 A CA 1076895A CA 254881 A CA254881 A CA 254881A CA 1076895 A CA1076895 A CA 1076895A
- Authority
- CA
- Canada
- Prior art keywords
- magnetic recording
- recording medium
- copolyester
- poly
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/66—Polyesters containing oxygen in the form of ether groups
- C08G63/668—Polyesters containing oxygen in the form of ether groups derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/672—Dicarboxylic acids and dihydroxy compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/16—Dicarboxylic acids and dihydroxy compounds
- C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
- C08G63/199—Acids or hydroxy compounds containing cycloaliphatic rings
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J167/00—Adhesives based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Adhesives based on derivatives of such polymers
- C09J167/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
- C09J167/025—Polyesters derived from dicarboxylic acids and dihydroxy compounds containing polyether sequences
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/90—Magnetic feature
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31678—Of metal
- Y10T428/31681—Next to polyester, polyamide or polyimide [e.g., alkyd, glue, or nylon, etc.]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31786—Of polyester [e.g., alkyd, etc.]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31786—Of polyester [e.g., alkyd, etc.]
- Y10T428/31797—Next to addition polymer from unsaturated monomers
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Paints Or Removers (AREA)
Abstract
912, 318 ABSTRACT
Magnetic recording tape, the binder of Which segmented copolyester of crystallizable ester units and amorphous ester units
Magnetic recording tape, the binder of Which segmented copolyester of crystallizable ester units and amorphous ester units
Description
: 912,318 MAGNETIC RECORDING MEDIUM
HAVING SEGMENTED COPOLYESTER BINDER
This invention concerns a magnetic recording medium, the recording layer of which consists of magnetizable particles in an improved organic binder.
Nearly all magnetic recording media have a surface layer consisting essentially of magnetizable particles dis-persed in nonmagnetizable binder. To permit recovery and re-use of solvents from which the binder is coated, the solvents should be capable of repeated distillation without chemical change. In this respect, aromatic solvents such as toluene lG and xylene are superior to the ketones. Ease of solvent recovery is enhanced if only one solvent is present, but ; it has been difficult to obtain use~ully smooth dispersions of magnetic pigment when using only one solvent with some of the binders of the prior art.
A widely used binder material is phenoxy resin which is a high molecular weight thermoplastic copolymer of -equivalent amounts of bisphenol A and the diglycidyl ether of bisphenol A such as is sold by Union Carbide Corporation as P~HH. To provide flexibility, the phenoxy resin may be blended with polyurethane. To provide good wear resistance and resistance to blocking at elevated temperatures, the binder polymers are crosslinked, primarily during the drying step, but the crosslinking reactions tend to continue for some time after the tape or other medium has cooled to ambient temperature.
The crosslinking involves a number of problems.
First, there is the problem of maintaining adequate pot- ;~
life. Second, it is desirable that the polishing step, to which most recording tapes are subjected, be carried out after the coating has been dried but before the binder ~ t~R~
.
107689~;
becomes fully crosslinked. The proper timing can be diffi-cult to control. Furthermore, difficulties in slitting are sometimes encountered after a phenoxy-urethane binder has fully cured.
Even though crosslinking involves problems, mag-netic recording tapes of the prior art employing uncross-linked binders, such as vinYl resins, have not provided equivalent resistance to wear. Such tapes have also ex-hibited poor resistance to blocking after exposure to high temperatures, especially if polished to the high degree of smoothness required for many applications.
The present invention concerns a thermoplastic -binder that without crosslinking provides magnetizable coatings which are equivalent to crosslinked phenoxy-urethane coatings in resistance to wear and to blocking at elevated temperatures. Because the binder need not be crosslinked, the above-discussed problems such as uncertain pot-life are avoided. Furthermore, the thermoplastic binder can generally be used with a single solvent such as toluene which with-stands repeated distillation without chemical change.
The benefits are accomplished by using as thebinder a thermoplastic segmented copolyester normally con-sisting essentially of about 25 to 75 per cent by weight of amorphous ester units and 75 to 25 per cent by weight of crystallizable ester units joined through ester linkages, the crystallizable ester units being of the formula:
~, ~, and the amorphous ester units being of the formula:
.
~ '~0761995 In these formulae, Rl is primarily tetramethyléne, phenylene and/or naphthalene and may in significant proportion be dimethylene, hexamethylene and/or octamethylene. To enhance solubility of the copolyester where Rl is entirely aromatic, the copolyester preferably contains at least 50 per cent by weight of amorphous ester units. Adipic acid is especially useful and may be used by itself or in combination with such dicarboxylic acids as sebacic acid, succinic acid~ suberic acid for making the segmented copolyester. To obtain phenylene radicals the dimethyl ester of the aromatic dicarboxylic acid should be employed to permit the condensation reaction to proceed at moderately elevated temperatures.
R2 consists of divalent radicals remaining after removal of the hydroxyl groups of one or more saturated aliphatic diols containing 2 to 12 carbon atoms, preferably 4 to 8. A particularly useful starting material is 1,4-cyclohexanedimethanol. Other representative saturated !
aliphatic diols include 1,3-butanediol, 1,5-pentanediol,
HAVING SEGMENTED COPOLYESTER BINDER
This invention concerns a magnetic recording medium, the recording layer of which consists of magnetizable particles in an improved organic binder.
Nearly all magnetic recording media have a surface layer consisting essentially of magnetizable particles dis-persed in nonmagnetizable binder. To permit recovery and re-use of solvents from which the binder is coated, the solvents should be capable of repeated distillation without chemical change. In this respect, aromatic solvents such as toluene lG and xylene are superior to the ketones. Ease of solvent recovery is enhanced if only one solvent is present, but ; it has been difficult to obtain use~ully smooth dispersions of magnetic pigment when using only one solvent with some of the binders of the prior art.
A widely used binder material is phenoxy resin which is a high molecular weight thermoplastic copolymer of -equivalent amounts of bisphenol A and the diglycidyl ether of bisphenol A such as is sold by Union Carbide Corporation as P~HH. To provide flexibility, the phenoxy resin may be blended with polyurethane. To provide good wear resistance and resistance to blocking at elevated temperatures, the binder polymers are crosslinked, primarily during the drying step, but the crosslinking reactions tend to continue for some time after the tape or other medium has cooled to ambient temperature.
The crosslinking involves a number of problems.
First, there is the problem of maintaining adequate pot- ;~
life. Second, it is desirable that the polishing step, to which most recording tapes are subjected, be carried out after the coating has been dried but before the binder ~ t~R~
.
107689~;
becomes fully crosslinked. The proper timing can be diffi-cult to control. Furthermore, difficulties in slitting are sometimes encountered after a phenoxy-urethane binder has fully cured.
Even though crosslinking involves problems, mag-netic recording tapes of the prior art employing uncross-linked binders, such as vinYl resins, have not provided equivalent resistance to wear. Such tapes have also ex-hibited poor resistance to blocking after exposure to high temperatures, especially if polished to the high degree of smoothness required for many applications.
The present invention concerns a thermoplastic -binder that without crosslinking provides magnetizable coatings which are equivalent to crosslinked phenoxy-urethane coatings in resistance to wear and to blocking at elevated temperatures. Because the binder need not be crosslinked, the above-discussed problems such as uncertain pot-life are avoided. Furthermore, the thermoplastic binder can generally be used with a single solvent such as toluene which with-stands repeated distillation without chemical change.
The benefits are accomplished by using as thebinder a thermoplastic segmented copolyester normally con-sisting essentially of about 25 to 75 per cent by weight of amorphous ester units and 75 to 25 per cent by weight of crystallizable ester units joined through ester linkages, the crystallizable ester units being of the formula:
~, ~, and the amorphous ester units being of the formula:
.
~ '~0761995 In these formulae, Rl is primarily tetramethyléne, phenylene and/or naphthalene and may in significant proportion be dimethylene, hexamethylene and/or octamethylene. To enhance solubility of the copolyester where Rl is entirely aromatic, the copolyester preferably contains at least 50 per cent by weight of amorphous ester units. Adipic acid is especially useful and may be used by itself or in combination with such dicarboxylic acids as sebacic acid, succinic acid~ suberic acid for making the segmented copolyester. To obtain phenylene radicals the dimethyl ester of the aromatic dicarboxylic acid should be employed to permit the condensation reaction to proceed at moderately elevated temperatures.
R2 consists of divalent radicals remaining after removal of the hydroxyl groups of one or more saturated aliphatic diols containing 2 to 12 carbon atoms, preferably 4 to 8. A particularly useful starting material is 1,4-cyclohexanedimethanol. Other representative saturated !
aliphatic diols include 1,3-butanediol, 1,5-pentanediol,
2-methyl-2,4-pentanediol, 1,6-hexanediol and 1,8-octanediol.
R3 is Rl or R5 where R5 consists of divalent radicals remaining after the removal of the carboxyl groups of saturated aliphatic dimer acids and includes 22 to 50 carbon atoms exclusive of the carboxyl groups originally present in the dimer acid. A readily available source is the hydrogenated form of the &36 di~er acid derived from ~ linoleic acid.
- R4 is R2 or R6 where R6 consists of divalent radicals remaining after removal of the terminal hydroxyl groups of long chain aliphatic diols having average molecular 30 weights of 200 to 4000. Among useful starting materials are 10761~9~
polyetherglycols such as poly(oxyethylene)glycols, poly(oxy-propylene)glycols, poly(oxytetramethylene)glycols and random or block copolymers thereof; poly(lactone)glycols, e.g., poly(caprolactone)glycol; poly(oxyalkylenecarbonate)glycols, e.g., poly(oxyethylenecarbonate)glycol; and glycols containing a hydrocarbon main chain, e.g., hydroxy-terminated poly-butadiene.
At least one of R3`and R4 in the amorphous ester unit is R5 or R6. If only one of R3 and R4 is R5 or R6, it is easier to predict the properties of the segmented copolyester. Where both R3 and R4 are primarily R5 and R6, respectively, the copolyester should comprise at least about 45 per cent by weight of crystallizable ester units to pro-vide magnetizable coatings having good resistance to wear and to blocking at elevated temperatures.
Small amounts of other materials which do not inter-fere with the polymerization reaction to form the segmented copolyester can be present. In any event, Rl, R2, R3, R4 and any other building block should be selected such that the segmented copolyester has a differential thermal analysis (DTA) melting temperature of from about 65 to 150C and an inherent viscosity of at least 0.5 dl/g at 25C, as measured ~ in 0.3 g/dl solution of the copolyester in chloroform at 25C. -; The DTA glass transition temperature, Tg, should be less than 0C. The DTA melting temperature is measured in an atmosphere of helium at a temperature rise of 30C/minute, the test ordinarily being run over the range of about -140 to +200C.
Those segmented copolyesters which are all or nearly all aliphatic dissolve readily in toluene or xylene and can be used with only one of these or other common - . : ,- . ; , - .: : ,; ; :, . .
~7~8~5 organic solvents in the manufacture of magnetic recording tapes. Other solvents for the segmented copolyester which provide solutions of usefully high solids content (e.g., 30-35% by weight) for applying magnetizable coatings include diacetone alcohol, isopropyl alcohol, cyclohexanone and tetrahydrofuran. Where Rl is all or nearly all aromatic, a preferred solvent is cyclohexanone, and it may be desira-ble to employ a mixture of solvents to obtain the desired coating consistency. While high aromatic content renders the segmented copolyester somewhat more resistant to heat, the advantage of using a single solvent such as toluene may make it desirable that Rl be appreciably aliphatic.
The segmented copolyesters can be prepared by conventional polycondensation polyester-forming reactions wherein one or more short chain diacids and/or long chain diacids or their equivalents (e.g., alcohol esters, acid chlorides, or anhydrides of the diacids) are caused ~o react with an equivalent amount of one or more short chain diols and/or long chain diols. Since copolymers of relatively high molecular weight are desired, it is pref-erable that the reaction be carried out in the presence ~
of a suitable antioxidant and catalyst. ;
A magnetic recording medium of the present inven-tion generally comprises a nonmagnetic backing member bear-ing a coating comprising a major proportion by weight ofmagnetizable particles, such as acicular gamma-Fe203 particles or acicular CrO2 particles, and a minor proportion of the segmented copolyester as the binder. The backing member may be a lexible plastic film as used in tapes or diskettes or a rigid material such as an aluminum ~07~8gS
sheet used in disk packs or a semi-rigid material such as vinyl card stock used in credit cards. Because the highly loaded segmented copolyester does not adhere well to biaxially-oriented polyethylene terephthalate film, it may be desirable to first apply to the backing member a very thin coating o~ an adhesion-promoting primer such as the aminized reaction product of an epoxidized polybutadiene as disclosed in U. S. patent No. 3,661,874 (Olson). Another B useful primer coating has been provided by a vinyl res n containing pendant hydroxyl groups (Union Carbide VROH) ~hrough which it is crosslinked by an isocyanate.
Because the segmented copolyester is very strong and tough, it has been used to make a thin~ self-sustaining film comprising a major proportion by weight of magnetizable particles. The film was sufficiently tough to withstand creasing without fracture. Such a film may be laminated to credit-card stock as a magnetic recording stripe, the copolyester serving as its own adhesive.
Surprisingly, in view of the fact that no cross-linking is necessary, magnetic recording tapes of the presentinvention withstand adverse conditions of use as well as do tapes of the prior art having crosslinked phenoxy-urethane binders. For comparative studies, tapes of the present invention have been prepared using as the backing a poly-ethylene terephthalate film of 40 micrometers thicknesswhich has been biaxially oriented about 3X in each direction and employing conventional acicular gamma-Fe2O3 particles at 75% loading by weight to provide an Hc in the longitudinal direction of 300-320 oersteds. The following tests are especially meaningful for applications involving high-speed travel of the tape across magnetic heads:
~ e ~ ~
` 10768~315 Squareness The ~r/0max or the s~uareness of the hysteresis loop at 3000 oersteds applied field using a 60-cycle M-H
meter should normally exceed-0.75.
Distributin Value (Gn) Gn is determined by differentiating the afore-mentioned hysteresis loop and is the ratio of Hc/~ H where ~H is the width of the differentiated hysteresis loop at one-half its peak height. Gn should normally exceed 2Ø
Wear A tape 1.27 cm in width is spliced to form a 91.5-cm loop which is driven in contact with a set of four magnetic recording heads under a tension of 482 grams at a speed of 36.6 meters per second. The tape is weighed before and a ter a 10-minute test. A weight loss of less than 5 mg is considered to show satisfactory resistance to wear. This test is normally run in comparison to a standard instrumenta- `
tion tape such as No. 888 of Minnesota Mining and Manufacturing Company or other commercially available instrumentation tapes which are known to experience a weight loss of less than 5 mg.
; Resistance to Blocking A length of the tape 1.27 cm in width and 91.5 cm in length is wound upon itself on a 1.27-cm-diameter stain-less steel mandrel under two kilograms tension. After 18 hours in an air-circulating oven at 65C and 80% relative humidity, the tape is unwound and inspected. If no de-lamination is found, the tape is considered "Good". If there are only traces of delamination, the tape is con-sidered "Fair".
~07~89S
In general, recording tapes of the invention have excellent resistance to blocking. However, if an otherwise desirable tape of the invention has only "Fair" resistance to blocking, this can be improved by overcoating the mag-netizable layer with a very thin coating of highly fluorinatedalkyl polyethers such as "Krytox" 143 of E. I. du Pont de Nemours & Co. applied from a 1% solution.
Modulus The dynamic modulus of the tape coating is measured on the Rheovibron tester over a temperature range of 0 to 70C and should be fairly constant over the full temperature range and preferably below 5 x 101 dynes/cm2. Above that value, there is a tendency for the magnetizable coating to abrade to an undue extent when subjected to a high speed wear test.
,.
Segmented Copolyester A
Copolyester A is prepared using a 90/10 mol ratio of adipic acid and sebacic acid and a 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxytetramethylene)glycol of 990 molecular weight.
A 3-neck flask is fitted with a mechanical stirrer, a Dean-Starke~trap-condenser, a thermometer, ~ `
and a gas inlet for maintaining an inert atmosphere with-in the flask. Equivalent amounts of diacids and diols were charged to the flask as follows:
~t~e~a~
.. ~ . . . .. . . . ... .
~76895 Parts by weight 34.5 Adipic acid 5.3 Sebacic acid 34.2 1,4-cyclohexanedimethanol (approximately 70:30 trans:cis mixture of isomers) 26.0 Poly(oxytetramethylene)glycol (990 molecular weight) B o 1 Antioxidant (Clba Geigy ~Irganox~ 1010)-Inert gas is introduced into the flask and the 10 contents of the flask brought to 170C by means of a heated ;
oil bath. The mixture is stirred and held at this tempera~
- ture for about three hours. During this time, water ~`
resulting from the condensation is collected in the trap.
The temperature of the mixture is reduced to about 145C, and the pressure is then reduced to 5 to 0.25 mm Hg. These conditions are maintained for about one hour to remove additional volatile material. About 0.1 part of tetra-butyl titanate catalyst is then added while maintaining an ~nert atmosphere. The temperature of the mixture is in-creased to 200 to 220C and the pressure reduced to 0.15 ;
mm ~g and these conditions maintained for approximately` ~-4 hours. ~
The resultant segmented copolyester, which comprises -by weight 68.2% crystallizable ester units and 31.8% amorphous ester units, solidifies to a tough, flexible, colorless, opaque material having an inherent viscosity of o.8 dl/g, a melt temperature (Tm) of about 79C, a glass transition temperature (Tg) of -72C and an acid number (or value) of 2Ø
8gs Segmented Copolyesters B-D
Copolyesters B-D are prepared in the same way from equivalent amounts of diacids and diols as follows:
Copolyester B: Adipic acid plus 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxy-tetramethylene)glycol of 990 average molecular weight. , Copolyester C: Adipic acid plus 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxy-tetramethylene)glycol of 2000 average ` molecular weight.
`~ Copolyester D: 85/15 mol ratio of adipic acid and sebacic ~;
acid plus 90/10 mol ratio of 1,4-cyclo-hexanedimethanol and poly(oxytetramethylene)-glycol of 990 average molecular weight.
Example 1 Polyethylene terephthalate film of 25 microns in ~hickness which had been biaxially oriented about 3X in each direction and heat set was used as the backing member of a typical magnetic recording tape of the invention. To improve the adhesion of the magnetizable coating, the backing was first primed with a solution of an aminized reaction product ~~
of an epoxidized polybutadiene (U. S. patent No. 3,661,874).
Over the primer coating was applied a 33.7% solids dispersion in cyclohexanone containing the following:
Parts by weight Acicular gamma-Fe203 particles ................. 70.73 Phosphate anionic dispersing agent .............. 3.54 Aluminum oxide .................................. 1.13 Conductive carbon black ......................... 4.24 Copolyester A .................................. 19.30 Fatty acid derivative lubricant ................. 1.06 :L07615~$
The dispersion was prepared as follows: The gamma-Fe203 particles, the dispersing agent and the aluminum oxide were milled together with 64 g of cyclohexanone (54% solids) on B a Red Devil shaker in a 0.95-liter Quickie Mill containing 1800 grams of 0.3 cm milling media (steel spheres) for 45 minutes. The carbon black and 55 g of cyclohexanone (total solids 40%) were then added and milling was continued for an additional 15 minutes. ~inally, 96.5 g of a 20%
solution of the copolyester in cyclohexanone and the lubricant were added and the milling was continued for an additional 15 minutes.
The dispersion was applied over the primer coating using a gravure roll having a knurl of 127 lines per cm.
The coating was dried in an air-circulating oven for about 0.5 minute at 82C followed by one minute at 104C. Within about one hour, the surface was polished to an average peak-to-peak roughness of about 0.12-0.20 micrometer (using a Bendix Proficorder Model No. 5, 2.5-micrometer stylus).
The tape was slit to widths of 1.27 cm for testing.
Examples 2-4 - Example 1 was followed except for the substitu-tion of 19.30 parts by weight of each of the indicated segmented copolyesters as follows:
Segmented Example Copolyester
R3 is Rl or R5 where R5 consists of divalent radicals remaining after the removal of the carboxyl groups of saturated aliphatic dimer acids and includes 22 to 50 carbon atoms exclusive of the carboxyl groups originally present in the dimer acid. A readily available source is the hydrogenated form of the &36 di~er acid derived from ~ linoleic acid.
- R4 is R2 or R6 where R6 consists of divalent radicals remaining after removal of the terminal hydroxyl groups of long chain aliphatic diols having average molecular 30 weights of 200 to 4000. Among useful starting materials are 10761~9~
polyetherglycols such as poly(oxyethylene)glycols, poly(oxy-propylene)glycols, poly(oxytetramethylene)glycols and random or block copolymers thereof; poly(lactone)glycols, e.g., poly(caprolactone)glycol; poly(oxyalkylenecarbonate)glycols, e.g., poly(oxyethylenecarbonate)glycol; and glycols containing a hydrocarbon main chain, e.g., hydroxy-terminated poly-butadiene.
At least one of R3`and R4 in the amorphous ester unit is R5 or R6. If only one of R3 and R4 is R5 or R6, it is easier to predict the properties of the segmented copolyester. Where both R3 and R4 are primarily R5 and R6, respectively, the copolyester should comprise at least about 45 per cent by weight of crystallizable ester units to pro-vide magnetizable coatings having good resistance to wear and to blocking at elevated temperatures.
Small amounts of other materials which do not inter-fere with the polymerization reaction to form the segmented copolyester can be present. In any event, Rl, R2, R3, R4 and any other building block should be selected such that the segmented copolyester has a differential thermal analysis (DTA) melting temperature of from about 65 to 150C and an inherent viscosity of at least 0.5 dl/g at 25C, as measured ~ in 0.3 g/dl solution of the copolyester in chloroform at 25C. -; The DTA glass transition temperature, Tg, should be less than 0C. The DTA melting temperature is measured in an atmosphere of helium at a temperature rise of 30C/minute, the test ordinarily being run over the range of about -140 to +200C.
Those segmented copolyesters which are all or nearly all aliphatic dissolve readily in toluene or xylene and can be used with only one of these or other common - . : ,- . ; , - .: : ,; ; :, . .
~7~8~5 organic solvents in the manufacture of magnetic recording tapes. Other solvents for the segmented copolyester which provide solutions of usefully high solids content (e.g., 30-35% by weight) for applying magnetizable coatings include diacetone alcohol, isopropyl alcohol, cyclohexanone and tetrahydrofuran. Where Rl is all or nearly all aromatic, a preferred solvent is cyclohexanone, and it may be desira-ble to employ a mixture of solvents to obtain the desired coating consistency. While high aromatic content renders the segmented copolyester somewhat more resistant to heat, the advantage of using a single solvent such as toluene may make it desirable that Rl be appreciably aliphatic.
The segmented copolyesters can be prepared by conventional polycondensation polyester-forming reactions wherein one or more short chain diacids and/or long chain diacids or their equivalents (e.g., alcohol esters, acid chlorides, or anhydrides of the diacids) are caused ~o react with an equivalent amount of one or more short chain diols and/or long chain diols. Since copolymers of relatively high molecular weight are desired, it is pref-erable that the reaction be carried out in the presence ~
of a suitable antioxidant and catalyst. ;
A magnetic recording medium of the present inven-tion generally comprises a nonmagnetic backing member bear-ing a coating comprising a major proportion by weight ofmagnetizable particles, such as acicular gamma-Fe203 particles or acicular CrO2 particles, and a minor proportion of the segmented copolyester as the binder. The backing member may be a lexible plastic film as used in tapes or diskettes or a rigid material such as an aluminum ~07~8gS
sheet used in disk packs or a semi-rigid material such as vinyl card stock used in credit cards. Because the highly loaded segmented copolyester does not adhere well to biaxially-oriented polyethylene terephthalate film, it may be desirable to first apply to the backing member a very thin coating o~ an adhesion-promoting primer such as the aminized reaction product of an epoxidized polybutadiene as disclosed in U. S. patent No. 3,661,874 (Olson). Another B useful primer coating has been provided by a vinyl res n containing pendant hydroxyl groups (Union Carbide VROH) ~hrough which it is crosslinked by an isocyanate.
Because the segmented copolyester is very strong and tough, it has been used to make a thin~ self-sustaining film comprising a major proportion by weight of magnetizable particles. The film was sufficiently tough to withstand creasing without fracture. Such a film may be laminated to credit-card stock as a magnetic recording stripe, the copolyester serving as its own adhesive.
Surprisingly, in view of the fact that no cross-linking is necessary, magnetic recording tapes of the presentinvention withstand adverse conditions of use as well as do tapes of the prior art having crosslinked phenoxy-urethane binders. For comparative studies, tapes of the present invention have been prepared using as the backing a poly-ethylene terephthalate film of 40 micrometers thicknesswhich has been biaxially oriented about 3X in each direction and employing conventional acicular gamma-Fe2O3 particles at 75% loading by weight to provide an Hc in the longitudinal direction of 300-320 oersteds. The following tests are especially meaningful for applications involving high-speed travel of the tape across magnetic heads:
~ e ~ ~
` 10768~315 Squareness The ~r/0max or the s~uareness of the hysteresis loop at 3000 oersteds applied field using a 60-cycle M-H
meter should normally exceed-0.75.
Distributin Value (Gn) Gn is determined by differentiating the afore-mentioned hysteresis loop and is the ratio of Hc/~ H where ~H is the width of the differentiated hysteresis loop at one-half its peak height. Gn should normally exceed 2Ø
Wear A tape 1.27 cm in width is spliced to form a 91.5-cm loop which is driven in contact with a set of four magnetic recording heads under a tension of 482 grams at a speed of 36.6 meters per second. The tape is weighed before and a ter a 10-minute test. A weight loss of less than 5 mg is considered to show satisfactory resistance to wear. This test is normally run in comparison to a standard instrumenta- `
tion tape such as No. 888 of Minnesota Mining and Manufacturing Company or other commercially available instrumentation tapes which are known to experience a weight loss of less than 5 mg.
; Resistance to Blocking A length of the tape 1.27 cm in width and 91.5 cm in length is wound upon itself on a 1.27-cm-diameter stain-less steel mandrel under two kilograms tension. After 18 hours in an air-circulating oven at 65C and 80% relative humidity, the tape is unwound and inspected. If no de-lamination is found, the tape is considered "Good". If there are only traces of delamination, the tape is con-sidered "Fair".
~07~89S
In general, recording tapes of the invention have excellent resistance to blocking. However, if an otherwise desirable tape of the invention has only "Fair" resistance to blocking, this can be improved by overcoating the mag-netizable layer with a very thin coating of highly fluorinatedalkyl polyethers such as "Krytox" 143 of E. I. du Pont de Nemours & Co. applied from a 1% solution.
Modulus The dynamic modulus of the tape coating is measured on the Rheovibron tester over a temperature range of 0 to 70C and should be fairly constant over the full temperature range and preferably below 5 x 101 dynes/cm2. Above that value, there is a tendency for the magnetizable coating to abrade to an undue extent when subjected to a high speed wear test.
,.
Segmented Copolyester A
Copolyester A is prepared using a 90/10 mol ratio of adipic acid and sebacic acid and a 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxytetramethylene)glycol of 990 molecular weight.
A 3-neck flask is fitted with a mechanical stirrer, a Dean-Starke~trap-condenser, a thermometer, ~ `
and a gas inlet for maintaining an inert atmosphere with-in the flask. Equivalent amounts of diacids and diols were charged to the flask as follows:
~t~e~a~
.. ~ . . . .. . . . ... .
~76895 Parts by weight 34.5 Adipic acid 5.3 Sebacic acid 34.2 1,4-cyclohexanedimethanol (approximately 70:30 trans:cis mixture of isomers) 26.0 Poly(oxytetramethylene)glycol (990 molecular weight) B o 1 Antioxidant (Clba Geigy ~Irganox~ 1010)-Inert gas is introduced into the flask and the 10 contents of the flask brought to 170C by means of a heated ;
oil bath. The mixture is stirred and held at this tempera~
- ture for about three hours. During this time, water ~`
resulting from the condensation is collected in the trap.
The temperature of the mixture is reduced to about 145C, and the pressure is then reduced to 5 to 0.25 mm Hg. These conditions are maintained for about one hour to remove additional volatile material. About 0.1 part of tetra-butyl titanate catalyst is then added while maintaining an ~nert atmosphere. The temperature of the mixture is in-creased to 200 to 220C and the pressure reduced to 0.15 ;
mm ~g and these conditions maintained for approximately` ~-4 hours. ~
The resultant segmented copolyester, which comprises -by weight 68.2% crystallizable ester units and 31.8% amorphous ester units, solidifies to a tough, flexible, colorless, opaque material having an inherent viscosity of o.8 dl/g, a melt temperature (Tm) of about 79C, a glass transition temperature (Tg) of -72C and an acid number (or value) of 2Ø
8gs Segmented Copolyesters B-D
Copolyesters B-D are prepared in the same way from equivalent amounts of diacids and diols as follows:
Copolyester B: Adipic acid plus 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxy-tetramethylene)glycol of 990 average molecular weight. , Copolyester C: Adipic acid plus 90/10 mol ratio of 1,4-cyclohexanedimethanol and poly(oxy-tetramethylene)glycol of 2000 average ` molecular weight.
`~ Copolyester D: 85/15 mol ratio of adipic acid and sebacic ~;
acid plus 90/10 mol ratio of 1,4-cyclo-hexanedimethanol and poly(oxytetramethylene)-glycol of 990 average molecular weight.
Example 1 Polyethylene terephthalate film of 25 microns in ~hickness which had been biaxially oriented about 3X in each direction and heat set was used as the backing member of a typical magnetic recording tape of the invention. To improve the adhesion of the magnetizable coating, the backing was first primed with a solution of an aminized reaction product ~~
of an epoxidized polybutadiene (U. S. patent No. 3,661,874).
Over the primer coating was applied a 33.7% solids dispersion in cyclohexanone containing the following:
Parts by weight Acicular gamma-Fe203 particles ................. 70.73 Phosphate anionic dispersing agent .............. 3.54 Aluminum oxide .................................. 1.13 Conductive carbon black ......................... 4.24 Copolyester A .................................. 19.30 Fatty acid derivative lubricant ................. 1.06 :L07615~$
The dispersion was prepared as follows: The gamma-Fe203 particles, the dispersing agent and the aluminum oxide were milled together with 64 g of cyclohexanone (54% solids) on B a Red Devil shaker in a 0.95-liter Quickie Mill containing 1800 grams of 0.3 cm milling media (steel spheres) for 45 minutes. The carbon black and 55 g of cyclohexanone (total solids 40%) were then added and milling was continued for an additional 15 minutes. ~inally, 96.5 g of a 20%
solution of the copolyester in cyclohexanone and the lubricant were added and the milling was continued for an additional 15 minutes.
The dispersion was applied over the primer coating using a gravure roll having a knurl of 127 lines per cm.
The coating was dried in an air-circulating oven for about 0.5 minute at 82C followed by one minute at 104C. Within about one hour, the surface was polished to an average peak-to-peak roughness of about 0.12-0.20 micrometer (using a Bendix Proficorder Model No. 5, 2.5-micrometer stylus).
The tape was slit to widths of 1.27 cm for testing.
Examples 2-4 - Example 1 was followed except for the substitu-tion of 19.30 parts by weight of each of the indicated segmented copolyesters as follows:
Segmented Example Copolyester
3 C
4 D
The magnetic recording tapes of the examples were subjected to the above-described tests together with a com-30 mercially available tape of the same general construction r ~ t~ks 1~76~5 as a "Control" except that the binder of the Control was a crosslinked phenoxy-urethane system.
Resistance Modulus Example Squareness Gn WearBlocking(dynes/cm2) 1 .78 2.5 1.8 mgGood 4.5 x 101 .~ 2 .75 2-3 ~ Good 1.7 x 101 3 .75 2.4 ~ Good 1,9 x 101 4 .79 2.1 3.0 mgFair 3.2 x 101 Control .76 2.1 3.2 mgFair 6.1 x 101 ~Not tested ~'
The magnetic recording tapes of the examples were subjected to the above-described tests together with a com-30 mercially available tape of the same general construction r ~ t~ks 1~76~5 as a "Control" except that the binder of the Control was a crosslinked phenoxy-urethane system.
Resistance Modulus Example Squareness Gn WearBlocking(dynes/cm2) 1 .78 2.5 1.8 mgGood 4.5 x 101 .~ 2 .75 2-3 ~ Good 1.7 x 101 3 .75 2.4 ~ Good 1,9 x 101 4 .79 2.1 3.0 mgFair 3.2 x 101 Control .76 2.1 3.2 mgFair 6.1 x 101 ~Not tested ~'
Claims (7)
1. Magnetic recording medium comprising a non-magnetizable backing member bearing a coating of magnetizable particles in a binder, which binder comprises a thermoplastic segmented copolyester consisting essentially of about 25 to 75 per cent by weight of amorphous ester units and 75 to 25 per cent by weight of crystallizable ester units joined through ester linkages, the crystallizable ester units being of the formula and the amorphous ester units being of the formula wherein R1 is primarily tetramethylene, phenylene or naphthalene, R2 consists of divalent radicals remaining after removal of the hydroxyl groups of one or more saturated aliphatic diols containing 2-12 carbon atoms, R3 is R1 or R5 where R5 consists of divalent radicals remaining after removal of the carboxyl groups of saturated aliphatic dimer acids and contains 22-50 carbon atoms, and R4 is R2 or R6 where R6 consists of divalent radicals remaining after removal of the terminal hydroxyl groups of long chain aliphatic diols having average molecular weights of 200-4000, at least one of R3 and R4 in each amorphous ester unit is R5 or R6, and said copolyester has a DTA melting temperature of from about 65° to 150°C, an inherent viscosity of at least 0.5 dl/g at 25°C, as measured in 0.3 g/dl solution in chloroform at 25°C, and a Tg less than 0°C.
2. Magnetic recording medium as defined in claim 1 wherein only one of R3 and R4 is R5 or R6.
3. Magnetic recording medium as defined in claim l wherein R1 and the adjacent carbonyl groups comprise primarily the divalent radical of adipic acid.
4. Magnetic recording medium as defined in claim l wherein R2 is cyclo-aliphatic and contains up to 8 carbon atoms.
5. Magnetic recording medium as defined in claim 1 wherein R3 is the divalent radical of C36 dimer acid.
6. Magnetic recording medium as defined in claim l wherein R4 is poly (oxyethylene)glycol, poly(oxypropylene)glycol, poly(oxytetramethylene)glycol or a copolymer thereof.
7. Magnetic recording medium as defined in claim l wherein R1 is essentially entirely aromatic and the copolyester comprises at least 50 per cent by weight of amorphous units.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/591,936 US4025694A (en) | 1975-06-30 | 1975-06-30 | Magnetic recording medium having segmented copolyester binder |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1076895A true CA1076895A (en) | 1980-05-06 |
Family
ID=24368585
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA254,881A Expired CA1076895A (en) | 1975-06-30 | 1976-06-15 | Magnetic recording medium having segmented copolyester binder |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4025694A (en) |
| CA (1) | CA1076895A (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4173506A (en) * | 1975-06-30 | 1979-11-06 | Minnesota Mining And Manufacturing Company | Bonding method utilizing polyester adhesive exhibiting "open time" |
| US4092256A (en) * | 1976-12-22 | 1978-05-30 | Goodson Keith S | Magnetic coating compositions |
| DE2925582A1 (en) * | 1979-06-25 | 1981-01-22 | Basf Ag | THERMOPLASTIC, SEGMENTED ELASTOMERS COPOLYAETHERESTERS AND THEIR USE AS ADHESIVE |
| US4281104A (en) * | 1980-02-15 | 1981-07-28 | The Goodyear Tire & Rubber Company | Linear random copolyester pigment binders |
| US4539389A (en) * | 1983-03-30 | 1985-09-03 | Teijin Limited | Biaxially oriented polyester film |
| JPS6169866A (en) * | 1984-09-12 | 1986-04-10 | Polyplastics Co | Composite material composition |
| US5178953A (en) * | 1990-01-12 | 1993-01-12 | Ampex Media Corporation | Magnetic recording media having a binder comprising a low molecular weight high glass transition temperature vinyl polymer |
| JP2569199B2 (en) * | 1990-04-11 | 1997-01-08 | 帝人株式会社 | Easy-adhesive polyester film and method for producing the same |
| US5885700A (en) * | 1995-09-18 | 1999-03-23 | Minnesota Mining And Manufacturing Company | Thermoplastic lens blocking material |
| US6126528A (en) * | 1995-09-18 | 2000-10-03 | 3M Innovative Properties Company | Preformed ophthalmic lens base block with textured surface |
| US5763075A (en) * | 1996-09-13 | 1998-06-09 | Minnesota Mining And Manufacturing Company | Polycaprolactone lens blocking material |
| US5827390A (en) * | 1995-09-18 | 1998-10-27 | Minnesota Mining And Manufacturing Company | Method of holding an ophthalmic lens blank |
| US20040094250A1 (en) * | 2002-11-14 | 2004-05-20 | Estes-Cox Corporation | Composite propellant compositions |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA793254A (en) * | 1968-08-27 | Kittler Wolfram | Production of magnetic recording media | |
| US3023192A (en) * | 1958-05-29 | 1962-02-27 | Du Pont | Segmented copolyetherester elastomers |
| US3512930A (en) * | 1969-05-07 | 1970-05-19 | Du Pont | Stabilized ferromagnetic chromium dioxide |
| US3651014A (en) * | 1969-07-18 | 1972-03-21 | Du Pont | Segmented thermoplastic copolyester elastomers |
| US3941904A (en) * | 1970-12-21 | 1976-03-02 | E. I. Du Pont De Nemours & Company | Method of applying adhesive coatings using segmented copolyester compositions |
| US3832314A (en) * | 1970-12-21 | 1974-08-27 | Du Pont | Segmented copolyester adhesive and coating compositions |
| US3766146A (en) * | 1971-03-18 | 1973-10-16 | Du Pont | Segmented thermoplastic copolyester elastomers |
| US3763109A (en) * | 1971-08-19 | 1973-10-02 | Du Pont | Segmented thermoplastic copolyesters |
| US3775373A (en) * | 1972-05-30 | 1973-11-27 | Du Pont | Segmented thermoplastic copolyesters |
| US3775374A (en) * | 1972-06-05 | 1973-11-27 | Du Pont | Thermoplastic copolyetheresters based on 2,6-naphthalene-dicarboxylic acid |
| US3775375A (en) * | 1972-06-20 | 1973-11-27 | J Wolfe | Thermoplastic copolyetheresters based on 2,6-naphthalene-dicarboxylic acid |
| US3932326A (en) * | 1973-02-20 | 1976-01-13 | E. I. Du Pont De Nemours And Company | Soft thermoplastic segmented copolyesters as pressure sensitive adhesives |
| US3891604A (en) * | 1973-11-29 | 1975-06-24 | Du Pont | Segmented thermoplastic copolyester elastomer |
| US3890279A (en) * | 1973-12-10 | 1975-06-17 | Du Pont | Thermoplastic copolyester elastomer |
-
1975
- 1975-06-30 US US05/591,936 patent/US4025694A/en not_active Expired - Lifetime
-
1976
- 1976-06-15 CA CA254,881A patent/CA1076895A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4025694A (en) | 1977-05-24 |
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