CA1136272A - Coated magnetic recording medium - Google Patents

Abstract

TITLE OF THE INVENTION:
Magnetic Recording Medium ABSTRACT OF THE DISCLOSURE:
A thin film type magnetic recording medium having a coating of ultraviolet ray setting epoxy resin containing a lubricant at least on one major surface. Degradation of resistance to wear may be minimized and stable recording and reproduction characteristics may be ensured even at high temperatures and at high humidity.

Description

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B.iC~GROI~D OF THE I;~VENTION: ~ .
The present invention relates ~o magnetic recording media having high resistance to wear.
Thln film type magnetic recording media are fabricated by ç~ating a thin ferromagnetic film on a base such as plastic film by the techniques of vacuum deposition, sputtering, ion plating and so on. Thin film type magnetic recording media or tapes are advantageous over the prior art coated type magnetic xecording media in that the thickness of ma~netic ~n film may be reduced by about one tenth of the thickness of the coated magnetic recording media so ~at they are adapted~ecially for use in high density n~rding such as recording o~ video signals. Hcwever ferromagnetic thin films are so hard that t~e wear and abrasion of a magnetic head results and the films themselves are also worn and abraised.
In order to overcome this problem, a protec iYe film must be formed on a ferromagnetic thin film. For instance, a m~no~
molecular film of lubricant such as stearic acid is formed or ~ ;~
a film o~ thermoplastic resins such as nylon including a lubricant is ~ormed. These prior art protective ~ilms exhibit 20 suffici2nt resistance to wear at relatively low temperatures and humidity such as at 20C and 50%, but the resistance to wear is considerably degraded at relatively high temperatures and humidity such as at 30 - 50C and at 80 - 90% so that the protectiv~ films are useless in practice, Environmental conditions under which home eguipment such ~s home video tape recorders, audio recorders and so on are used are not speciically determined. That i~, these equipment are oft~n used at relatively high temperatures and at high humidity. It follows theref~re that ferromagnetic thin films must be coated with a ,~ ' ' ' ~
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~L3~2 protective film which may e fe~tively prevent rapid wear and abrasion of both a magnetic head and a magnetic secording medium. :
Whe~ a ferromagnetic thin film is made on a base, he latter is heated in general in vacuum so that various additives present at the vicinity of the surfaces of the base are evaporated and removed. As a result, the uncoated sur- ;
face of the base lacks smoothness and exhibits in~reased insulation resistance so that triboelectric charging tends to ; :~
occur very freguently, In addition, the magnetic thin film become electrically conductive so that the transport of magnetic recording medium is sometimes hindered by electro-s:atic interference. These are the m~in reasons why ~he uncoated surfaces of magnetic recording media must be treated.

: 15 SU~RY OF TXE INVENTION: ~
Accordingly~ one of the objects of the present ~ :
invention is to pro~ide a magnetic recording medium whlch may exhibit hîgh resistance to wear and may maintain satisfactory ;~
recording and reproduction characteristics even at high temperatures and at high humidit~.
Ano~her object of the present inve~tion is to provide a magnetic recording medium whose at least one major surface is coated with a thin film of ultraviolet ray se~ting epoxy resins cont~ining a lubricant.
In accordance with the foregoing o~jects, there is provided~
A magnetic recording medium characteri~ed in that a ferromagnetic thin f~lm is used as a magnetic recording ilm or layer, and nt least one surface of said magnetic recording medium is co~ted with a thin film of ltraviolet ray setting ~ .
ep~xy resins containing a lubricant~

. ~ 3 DESCRIPTION OF THE PRE;FERRED EMBODI~ENTS.
The present invention relates to a magnetic record~
ing medium characterized in that it has a ferromagnetic thin : ' '.

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film as a magnetic recording layer and at least one of its major surfaces is coated with a thin film of ultraviolet ray setting epoxy resins containing a lubricant. Ultraviolet ray ~ ;~
setting epoxy resins are such that when they are irradiated ;~
with ultraviolet rays, ion polymer~3ation is initiated and the resins are set. A typical example consists unreacted epoxy resins, aromatic diazonium salts of complexes of halides which form Lewis acid when irradiated by ultraviolet rays and a gelation inhibitor which serves to neutralize Lewis acid formed by the thermal decomposition prior to the irradiation of ultraviolet rays. The epoxy resins of the type described ;
above are explained in detail in Japanese Laid Open Patent No. 49-121884.
Unreacted epoxy resins are bisphenol type epoxides `~
15 such as diglycidil ether of bisphenol A, polyglycidil ether ~ -of bisphenol A; cyclic aliphatic type epoxides such as 1,2-epoxycyclohexane,vinylcycIohexenedioxide~ 3,4-epoxycyclohexil~
methyl, 3'4'-epoxycyclohexenecarboxylate, 3,4-epoxy-6-methyl-cyclohexyl methyl, 3'4'-epoxy-6'-methylcyclohexenecarboxylate and so on; glycidilalkylether type epoxides such as glycidilphenylether and hexanedioldiglycidilether; and novorac type epoxides. The above epoxy resins!may be all used in the present invention, but most desirable effects may be obtained when the epoxy resin compound contains cyclic aliphatic 25 type epoxides in a quantity of more than one half based upon ~-the total weight.
Aromatic dizonium salts of complexes of halides ~ . .
which form Lewis acid when irradiated by ultraviolet rays are p-nitrobenzenediazoniumhexafluorophosphate, 2,5-dichloro~

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benzenediazoniumhexafluorophosphate, 2,4-dichlorobenzene diazoniumtetrafruoroborate, 4-(diamethylamino)-1-naphthalene -diazoniumhexafluorophosphate and so on.
Gelation inhibitors are cyclic amids such as 1-methyl-4-pyrrolidine, 1,-5-dimethyl-2-pyrrolidine and so on.
The protective film made from a comp~und consisting of 100 parts in weight of unreacted epoxy resins of the type described above, 0.5 to 5 parts by weight of a gelatin inhibitor was found to be unsatisfactory in smoothness so that the present invention further adds special lubricants as described in detail below.
Some of the lubricants used in plastic fabrication and of additives such as extreme-pressure agents added to ~.
lubricants have been found to attain very satisfactory results when used in the present invention. First type is aliphatic esters of polyhydric alcohols~such as ethylene glycol, glycerin, pentaerythritol, sorbitol and so on. For instance, they are available in the market as "POEM S-100" (aliphatic mono-glyceride), "S-120i' ~polyoxyethylene glycerin monostearate) and "S-250" (sorbitan stearate), all the products o RIKEN
VITAMIN KK.
Second type of the lubricants includes denatured silicons obtained by the chemical reactions between alkyl-polysiloxane on the one hand and polyhydric aliphatichydrocarbons, polyhydric aliphatic acids, polyhydric alcohols, alkyleneglycol, fluoroalkyl and so on the other hand. They are available in the market under the trademark of "PAINTATIVE ~`
DC-ll and FS-1265", the products of DOW CORNING CORP; under '-~

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the tradename of "SF-69 OIL", the product of GE Corp; under the trademark of "KP-3011' the product of SHINETSU KAGAKU KK' under the trademarks of "L-77", "L-7607" and "L-49", the products of NIPPON UNIKA KK. Third type includes denatured fluorine oils obtained by the chemical reactions between perfluoroalkyl on the one hand and polyhydric aliphatic acids, polyhydric alcohols, alkyleneglycol and so on, on the other hand. They are also available in the market under the trademarks of "FC-430" add "FC-431", the products of SUMITO
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3M KK; under the trademarks of "MEGAFAC F 120, F142D, F-171, F-177", the products of DAINIPPON INK KK. ~ -One or more types of lubricants descrihed above may be directly mixed with epoxy compounds. Alternatively, one or more types of lubricants may be dissolved into suitable solvents and added to epoxy compounds. It is preferable to add 0.01 to 20 parts by weight of one or more types of lubricants to 100 parts by weight of an epoxy resin compound.
In addition~to the above described lubricants, solid powder lubricants such as graphite, molybdenum disulfide, 20 carbon fluoride, tetrafluoroethylene and so on; and finely ~ -divided powder such as carbon powder, various organic pigments aluminum powder ~nd so on may be used. Furthermore suitable solvents may be added epoxy resin compounds in order to reduce .~:
their viscosity. Furthermore polymerization control agents, 25 antistatic agents, stabilizers, anticorrosion agents and so .
on may be added. When the solvents are evaporated prior to ~ -the irradiation of ultraviolet rays, there will be no adverse ~
~ ~ :
effects on hardening or setting.

A protective film of ultraYiolet ray setting epoxy : ~'' .,.~

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resins in accordance with the present invention may be directly formed on a ferromagnetic thin film of Co-P, Co, Co-Fe, Co-Ni, Fe-Ni coated on a base by the conventional techniques.
Alternatively, an anticorrosion film of Al, Cr and so on may be interposed between a protective film and a ferromagnetic thin film. In view of spacing loss of a magnetic head, it is preferable to control the thickness, after hardening, of the protective film to less than 0.5 micrometers or more preferably between 0.01 and 0.1 micrometers. Satisfactory results may ~ -be also achieved when a protective thin film is made on the uncoated or rear surface of a base to a thickness of between 0.01 and 0.1 micrometers. In this case, it is not needed to take the spacing loss into consideration so that a protective thin film may be from 0.5 to a few micrometers in thickness.
Even though the -epoxy resin protective thin films of the present invention are less than 0.1 micrometers in thickness, they exhibit excellent bonding strength and resistance to wear especially at high temperatures and high humidlty such as at 30 to 50C and at 80 to 90%. `
It is most pr#ferable to coat both the surfaces of a magnetic recording medium with protective thin films of the present invention, but it is to be understood that even when only one protective thin film is made on one surface of a ~`
magnetic recording medium, very satisfactory results may be obtained because the lubricants in the protective thin film are transferred or transplanted into the other surface when the magnetic recording medium or tape is wound.
Next same examples of the present invention will be described.

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EXAMPLE 1: -~
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A cobalt ferromagnetic thin film was coated to the ~ ~
thickness of 0.3 micrometers by the vacuum deposition techniques ~:
on a base of biaxially extended polyester film. Thereafter : ;
5 the compound of the composition described below ~as applied ~
by a photogravure coater on the ferromagnetic thin film to ~; :
the t~ickness of about four micrometers and the solvent was evaporated at 80C. Next the protective layer or thin film was irradiated for two seconds by the ultraviolet rays emitted from a straight ultraviolet ray lamp with the rated lamp power of 80 W/cm so that the protective layer or thin film was hardened. Thereafter the magnetic recording medium was cut into a tape with a suitable width, which will be referred to as "specimen A".
Composition : Parts by weight vinylcyclohexenedioxide 100 `
p-nitrobenzene diazoniumhexafluoxophosphate 1 :~
pentaerythritol tetrastearate acetone 2000 20 toluene 2000 ` :~' EXAMPLE 2: ~ .
Following the procedures of EXAMPLE 1, specimen B ~- ~
was prepared, but instead of the lubricant, pentaerythritol~ :, tetrastearate, denatured silicon available in the market under 25 the trademark of "KP-301", the product of SHINETSU KAGAKU KK, ,;. ;
was used, the quantity being 1 part. - -:
Following also the procedures of EXAMPLE 1, specime~

C was prepared, but as the lubricant, one part of "MEGAFAC

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~r F120", the product of DAINIPPON INK KK was used.
:
EXAMPLE 4:
Following the procedures of EXAMPLE 3, specimen D
was prepared, but the protective thin film was made on the rear surface of the base.
For the sake of comparison, two specimens E and F were also prepared. Specimen E was prepared by following ;
the procedures of EXAMPLE 1, but the lubricant, pentaerythritol tetrastearate was excluded.
Specimen F was prepared from a compound having the following composition.
Parts by weight `
polyamide resln (THOMIDE #395) 100 pentaerithritol tetrastearete 3 xylene. 3000 isopropylalcohol 3000 Instead of initiating the setting of the protective thin film with the irradiation of ultraviolet rays/ the protective thin film was subjected to heat treatment with the hot air of 120C.
These specimens A - F were subjected to still tests with a home video tape recorder placed in a thermohydrostat.
The test results are shown below.

_ , :.
Environmental conditionsStill time in minute _ , .,~
temperaturehumidity A B C D E F
in C in ~ -, ... ._ _ _ _ :~
20C 50~ 60 45 55 35 10 60 -__ _ _ _ ,. _ . :
20C 90% 50 30 45 4010 25 , ~ _ _ :
30C 40~ 60 30 55 3010 30 _ _ _ _ .. _.
30C 90% 45 25 40 25 5 5 " ~ _ _ . . _ _ ~ . . :
40C 90% ~ 4Q 25 35 25 5 1 _ _ _ ~

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~XAMPLE 5 A Co ferromagnetic thin film was made to the th.ickness ~
of 0.3 micrometexs by the techniques of vacuum deposition on ~ :
a base of tensilized polyester film 6 micrometers in thickness. ~:
S A protective thin film compound having the following composition . , was applied by a photogravure coater to the thickness of about four micrometers on both sides of over the ferromagnetic thin film.
CompositionParts by wei~ht ~:

10 3,4-epoxycyclohexylmethyl, 3'4'-epoxycyclohexenecarboxylate ~ 50 ;
hexanedioldiglycidilether 50 "L-77", the product of NIPPON UNIKA KK.
p-nitrobenzenediazoniumtetraphloroborate 5 :
15 ethyl acetate 4000 benzene 2000 .
: The solvents were evaporated at 80C and thereafter the protective thin fllm was hardened by irradiating for three : seconds with the ultraviolet rays emitted from a straight ultraviolet ray lamp with the rated power of 80 W/cm. The magnetic recording medium thus prepared was Cllt into tape with a suitable width, which are referred to as "specimen G". .~:~

: -:
Following the procedures of EXAMPLE 5, specimen H ..

was prepared, but the composition was changed as follows~

3,4-epoxycyclohexymethyl, :~
3',4'-epoxycyclohexenecarboxylate 40 parts by wPight hexanedioldiglycidiIether 60 parts by weight -. -The others remained unchanged. ~ ~

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For the sake of comparison, specimen I was prepared by following the procedures of EXAMPLE 5, but the composition of the protective thin film was changed as follows: ~ ~
Composition P ~ ;
5 vinylidenechloride acryl series copolymers ~;

"ALON CH-2", the product of TOA GOSEI
KAGAKU KK. 100 "L-77", the product of NIPPO~ UNIKA KK. 1 ~ .
Ethyl acetate 2000 Methylethylketon 1000 10 Toluene 1000 `
Furthermore instead of irradiating with the ultraviolet rays, :: :
the protective thin film was subjected to the drying step with the hot air of 120C. ~ `
The spe,cimens G, H and I were loaded into respective ~.
cassettes and tested with a micro-cassette tape recorder commercially available in the market. That is, recording and . ~
reproduction were repeatedly made at 40C and at 70% in humidity.
After 20 repeated recoxdings and reproductions, the specimen G showed no not,iceable change in characteristics. As to the - ,::
specimen H, after the 15-th run, the repxoduction output dropped slightly because of the contamination~of the reproducing head, but the stable transport was ensured up to the 20-th run. ~' As to the specimen I, the reproduction head was contaminated -even after the first run so that the reproduction output dr~pped remarkably. Furthermore the transport of the tape was not stable.
In summary, the magnetic recording media in accordance ~ -with the present invention may exhibit almost unchanged :~, resistance to wear and may maintain satisfactory recording and ~

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reprod~ction characteristics even at high temperatures and at high humidity. Thus they have very high values from the standpount of the industry.
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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A magnetic recording medium characterized in that a ferromagnetic thin film is used as a magnetic recording film or layer, and at least one surface of said magnetic recording medium is coated with a thin film of ultraviolet ray setting epoxy resins containing a lubricant.

2. A magnetic recording medium as set forth in Claim 1 further characterized in that said thin film of ultraviolet ray sett-ing epoxy resins containing a lubricant is made by applying a coating of a compound consisting essentially of unreacted epoxy resins, aromatic ziazonium salts of complexes of halides which form Lewis acid when irradiated by the ultraviolet rays, a gelatin inhibitor and a lubricant and by irradiating said coating with the ultraviolet rays, thereby setting or hardening the same.

3. A magnetic recording medium as set forth in Claim 2 further characterized in that said unreacted epoxy resins contain cyclic aliphatic type epoxy resins in a quantity more than one half by weight based on the total weight of said unreacted epoxy resins.

4. A magnetic recording medium as set forth in Claim 2 further characterized in that said lubricant is selected from a group consisting of aliphatic esters of polyhydric alcohols, denatured silicone and denatured fluoride oil.