JPH0727628B2 - Magnetic recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer.

[Background of the Invention and Description of Prior Art] Generally, as a magnetic recording medium for audio, video or computer (hereinafter also referred to as a magnetic tape), γ-Fe ₂ O ₃ , Co-containing magnetic iron oxide, A magnetic recording medium has been used in which a magnetic layer in which a ferromagnetic metal oxide powder composed of needle-like crystals such as CrO ₂ is dispersed in a binder width is provided on a non-magnetic support. Recently, however, the demand for high-density recording has increased, and magnetic tapes using ferromagnetic metal fine powder have been used in place of these ferromagnetic metal oxide powders.

Information is recorded and reproduced by traveling while the surface of the magnetic layer of such a magnetic recording medium is in contact with the magnetic head. Since this recording / reproduction is performed at extremely high speed and frequency, there is a strong demand for improving the running durability of the magnetic layer.

In order to obtain this running durability, a polyester type polyurethane resin having excellent wear resistance is generally used as a binder resin used for forming a magnetic layer. However, this type of polyurethane resin is susceptible to deterioration due to moisture, light, heat, etc., and when it is stored or used for a long period of time, for example, when it is stored under severe conditions such as being left in the interior of an automobile in the summer. In addition, since it decomposes into a low molecular weight compound, deterioration of the magnetic layer is liable to occur, and running durability, especially after long-term storage, was not sufficient.

Recently, a polycarbonate polyurethane resin has been attracting attention as a polyurethane resin in which the deterioration of this resin is improved, and an invention using this as a binder is disclosed in JP-A-58-60430 and JP-A-59-59. It is disclosed in, for example, 198530.

However, although the use of polycarbonate polyurethane as a binder can prevent lowering of the molecular weight due to hydrolysis, there are low molecular weight substances contained in the polycarbonate polyurethane or the resin used in combination as a binder at that time. Therefore, it cannot be said that the running durability is sufficiently excellent even if polycarbonate polyurethane is used as the binder.

[Object of the Invention] An object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and improved running durability.

In particular, it is an object of the present invention to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability after long-term storage.

SUMMARY OF THE INVENTION The present invention is a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder dispersed in the binder on the support, wherein the binder contains polycarbonate polyurethane, In addition, the magnetic recording medium is characterized in that the binder has a soluble fraction in tetrahydrofuran of 35 wt% or less after the curing treatment.

[Effects of the Invention] The magnetic recording medium obtained by the present invention exhibits not only excellent electromagnetic conversion characteristics but also improved running durability.

That is, the magnetic recording medium of the present invention contains, as a binder, polycarbonate polyurethane which is a polymer which is stable against moisture, light and heat, and the cured product of the binder has the above-mentioned particularly low content. It is a cured product with a low content of molecular weight substances. Therefore, since the generation of low molecular weight substances due to decomposition is small and the content of low molecular weight substances in the binder itself is low, various adverse effects caused by low molecular weight substances, that is, magnetic layers due to long-term storage or running Can be prevented from deteriorating. This can improve the electromagnetic conversion characteristics and the running durability.

Detailed Description of the Invention The magnetic recording medium of the present invention has a basic structure in which a non-magnetic support and a magnetic layer made of ferromagnetic powder dispersed in a binder are provided on the non-magnetic support. It is a thing.

The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of materials that form the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, polyimide, polysulfone, polyethersulfone, and other synthetic resin films, and aluminum. A metal foil such as a foil or a stainless foil can be used. The non-magnetic support used is generally 2.5 to 100 μm, preferably 3 to 70 μm.

The non-magnetic support may have a back layer (backing layer) provided on the side where the magnetic layer is not provided.

As described above, the magnetic recording medium of the present invention has a magnetic layer in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support.

Examples of the ferromagnetic powder used in the present invention include ferromagnetic iron oxide powder, Co-doped ferromagnetic iron oxide powder, ferromagnetic chromium dioxide powder, ferromagnetic metal powder, and barium ferrite. The acicular ratio of the ferromagnetic iron oxide powder and the ferromagnetic chromium dioxide powder is 2/1 to 20/1, preferably 5/1 or more, and the average major axis length is preferably in the range of 0.2 to 2.0 μm. The specific surface area (S BET) of the ferromagnetic powder is preferably 30 m ² / g or more.

The ferromagnetic metal fine powder is a ferromagnetic metal fine powder containing iron, cobalt or nickel and has an average major axis length of 1.0 μm.
The following fine particles have a specific surface area (S BET) of 4
It is preferably a ferromagnetic metal fine powder of 5 m ² / g or more.
When the specific surface area of the ferromagnetic metal fine powder is smaller than 45 m ² / g, it becomes difficult to obtain a target magnetic recording medium having high electromagnetic conversion characteristics.

As an example of this ferromagnetic metal fine powder, the metal content in the ferromagnetic metal fine powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one kind of ferromagnetic metal or alloy (eg, Fe , Co, Ni, Fe-Co, Fe-Ni, Co-Ni, Co-Ni-
Fe) and other components (eg, Al, Si, S, Sc, Ti, V, Cr, Mn, Cu, Zn) within the range of 20% by weight or less of the metal content.
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, A
u, Hg, Pb, Bi, La, Ce, Pr, Nd, B, P) may be included. Further, the ferromagnetic metal component may include a small amount of water, hydroxide or oxide. Methods for producing these ferromagnetic metal fine powders are already known, and the ferromagnetic metal fine powders used in the present invention can also be produced according to these known methods.

The shape of the ferromagnetic metal fine powder is not particularly limited, but needle-shaped, granular, dice-shaped, rice granular, and plate-shaped particles are usually used.

The content of the total binder in the magnetic layer of the magnetic recording medium of the present invention is usually 10 to 100 parts by weight, preferably 15 to 40 parts by weight, and particularly preferably 100 parts by weight of the ferromagnetic powder. Is 20 to 35 parts by weight.

In the magnetic recording medium of the present invention, the binder forming the magnetic layer contains polycarbonate polyurethane.

Polycarbonate polyurethane is synthesized by a reaction between a polycarbonate polyol and a polyisocyanate or a reaction between a polycarbonate polyester polyol synthesized from a polycarbonate polyol and a dicarboxylic acid and a polyisocyanate. At that time, if necessary, a chain extender can be used in the above reaction to obtain a polycarbonate polyurethane having desired physical properties. The above-mentioned polycarbonate polyol can be generally synthesized by the transesterification method of polyhydric alcohol and dialkyl carbonate or diallyl carbonate, or can be obtained by condensation of polyhydric alcohol and phosgene.

The polycarbonate polyurethane used in the present invention is not particularly limited and can be prepared according to the conventional method described above. Such a polycarbonate polyurethane is disclosed in JP-A-58-60430.

The dialkyl carbonate or diaryl carbonate and the polyisocyanate used when preparing the polycarbonate polyurethane according to the method described above are not particularly limited and those commonly used can be used.

In the polyhydric alcohol, R in the general formula [HO-R-OH] is: an alkylene group having 3 to 14 carbon atoms, And a diol containing a tertiary amino group in the molecular chain (general formula; [CnH ₂ n ₊₁ -NH
₂ (n = 1 to 20)] and diol and derivatives thereof obtained by adding 2 to 50 mol of ethylene oxide, propylene oxide and butylene oxide to the primary amine.

Examples of the polyhydric alcohol include 1,6-hexanediol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,3-pentanediol, 1,4-
Polyhydric alcohols such as cyclohexanedimethanol and glycerin can be used. Of these, 1,6-hexanediol and 1,4-cyclohexanedimethanol are preferred as diols and glycerin is preferred as triol.

The polycarbonate polyol obtained from the polyhydric alcohol and the carbonate or phosgene preferably has a molecular weight of 300 to 20,000 and a hydroxyl value of 20 to 300.

On the other hand, the polycarbonate polyester polyol is synthesized from the above polycarbonate polyol and dicarboxylic acids.

The dicarboxylic acids are represented by the general formula; [HOOCR'COOH], and R'is, for example, an alkylene group having 3 to 6 carbon atoms, Can be mentioned.

The polycarbonate polyester has a molecular weight of 400 to 3
And it is preferable that the hydroxyl value is in the range of 5 to 300.

In addition to these polycarbonate polyols and polycarbonate polyester polyols, ordinary polyols such as polyether polyols and polyester polyols may be used.

Examples of the polyisocyanate that reacts with the polyol include tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, cyclohexane diisocyanate, 2,4 tolylene diisocyanate, and 2,6 tolylene diisocyanate. , 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate and 1,5 naphthylene diisocyanate. Of these, 2,4 tolylene diisocyanate and 4,4 ′ diphenylmethane diisocyanate are preferable.

Polycarbonate polyurethane is synthesized by the reaction of the above polyol and polyisocyanate. At this time, if necessary, a chain extender can be used in the above reaction to obtain a polycarbonate polyurethane having desired physical properties.

Examples of the chain extender include the above-mentioned polyhydric alcohols, aliphatic polyamines, alicyclic polyamines and aromatic polyamines. Among these, polyhydric alcohols are preferable.

The polycarbonate polyurethane preferably has a molecular weight (number average molecular weight) of 10,000 to 120,000. When a polycarbonate polyurethane having a molecular weight of less than 10,000 is used, the running durability may not be sufficiently improved, and when a molecular weight of more than 120,000 is used, the solubility of the resin is poor and it is disadvantageous in production, which is not preferable. .

It is necessary that the binder of the present invention contains the above-mentioned polycarbonate polyurethane and that the binder has a soluble fraction in tetrahydrofuran of 35% by weight or less after the curing treatment.

Polycarbonate polyurethane contained in the above binder is a polymer which is stable to moisture, light and heat. The cured product of the binder is a cured product containing a small amount of the above-mentioned particular low molecular weight substance. Therefore, the production of low molecular weight substances due to decomposition is low, and since the content of low molecular weight substances in the binder itself is low, various adverse effects caused by the low molecular weight substances revealed by the present inventor, namely, long-term storage Alternatively, deterioration of the magnetic layer due to running can be prevented. As a result, electromagnetic conversion characteristics and running durability can be improved.

There are the following methods for reducing the soluble fraction of the binder in the tetrahydrofuran after the curing treatment.

1) Increase the amount of curing agent in the binder.

2) Polymerize the polycarbonate polyurethane and / or the combined resin.

3) Increase the glass transition point of the polycarbonate polyurethane and / or the combined resin.

4) Introduce cyclohexyldimethanol, hydroxypivaloyl group and the like into the polycarbonate polyurethane and / or the combined resin.

The method for reducing the soluble fraction is not limited to the above method. Other methods may be used.

The soluble fraction is measured by separating the magnetic layer from the magnetic recording medium and extracting the low molecular weight substance in the binder with tetrahydrofuran at 60 ° C.

Although the above-mentioned polycarbonate polyurethane can be used alone as a binder, it is usually used as a mixture with another binder. When used in combination with other binders, it is preferred to use the polycarbonate polyurethane in the range of 20 to 90% by weight of the total binder.

There is no particular limitation on the other binder used by mixing with the above polycarbonate polyurethane, examples of other binders include polyurethane resins other than the present invention, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate. With vinyl alcohol, maleic acid and / or acrylic acid, vinyl chloride / vinyl propionate copolymer, vinyl chloride / vinylidene chloride copolymer, vinyl chloride / acrylonitrile copolymer, ethylene / vinyl acetate copolymer Coalescing,
Nitricellulose resin, cellulose nitrate, cellulose acetate butyrate, cellulose derivative such as cellulose acetate propionate, acrylic resin,
Examples thereof include polyvinyl acetal resin, polyvinyl butyral resin, epoxy resin, and phenoxy resin.

These resins include acidic groups such as carboxylic acid, sulfinic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group, amino acid, aminosulfonic acid, sulfuric acid or phosphoric acid ester of aminoalcohol, in addition to main polar groups. Amphoteric groups such as alkyl betaine type, amino groups, imino groups,
Imido group, amide group and the like, and usually contains at least one hydroxyl group, alkosyl group, thiol group, halogen group, silyl group, siloxane group, and each polar group is 1 × 10 ^-6 to 1 g of resin.
It is preferably contained in the range of 1 × 10 ⁻³ equivalent. The other binder of the magnetic recording medium of the present invention is preferably a copolymer of vinyl chloride / vinyl acetate and vinyl alcohol, maleic acid and / or acrylic acid, and vinyl chloride / vinyl acetate / maleic acid copolymer. The combination is particularly preferable.

It is also possible to use a polyisocyanate compound in mixture with the above polycarbonate polyurethane. Examples thereof include reaction products of 3 mol of diisocyanates such as tolylene diisocyanate and xylylene diisocyanate and 1 mol of trimethylolpropane, and polymethylene polyphenyl polyisocyanates.

The magnetic layer of the magnetic recording medium of the present invention using a binder containing polycarbonate polyurethane has a Mohs hardness of 6
The above abrasives may be contained.

The abrasive used is not particularly limited as long as it has a Mohs hardness of 6 or more. Examples of abrasives include α-Fe ₂ O ₃ , Cr ₂ O ₃ ,
α-Al ₂ O ₃ and SiC can be mentioned, and these can be used alone or in combination.

The average particle size of the abrasive used is preferably in the range of 0.01 to 5.0 μm, and particularly preferably in the range of 0.1 to 1.0 μm.

The content of abrasive is usually 0.1 per 100 parts by weight of ferromagnetic powder.
To 20 parts by weight, preferably 1 to 10 parts by weight.

In addition to the above abrasives, the magnetic layer preferably contains carbon black (in particular, an average particle size of 10 to 300 mμ).

Next, an example of a method of manufacturing the magnetic recording medium of the present invention will be described.

First, a magnetic powder is prepared by kneading a ferromagnetic powder such as a ferromagnetic metal fine powder, a binder, and if necessary, an abrasive, a filler and the like with a solvent. As the solvent used at the time of kneading,
Solvents commonly used in the preparation of magnetic paints can be used.

The kneading method is not particularly limited, and the addition order of each component can be appropriately set.

For the preparation of the magnetic paint, a conventional kneading machine, for example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand glider, a Szegvari attritor,
Examples thereof include a high speed impeller disperser, a high speed stone mill, a high speed impact mill, a disper, a kneader, a high speed mixer, a homogenizer and an ultrasonic disperser.

When preparing the magnetic paint, known additives such as a dispersant, an antistatic agent and a lubricant may be used together.

The magnetic coating material thus prepared is applied onto the above-mentioned non-magnetic support. The coating can be performed directly on the non-magnetic support, but can also be performed on the non-magnetic support via an adhesive layer or the like.

Examples of the coating method on the non-magnetic support, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze cord, impregnation coat,
Reverse roll coat, transfer roll coat,
Examples thereof include a gravure coat method, a kiss coat method, a cast coat method, a spray coat method, and a spin coat method, and a method other than these methods can be used.

The thickness of the magnetic layer thus coated is generally in the range of about 0.5 to 10 μm, usually 1.5 to 7.0 μm, as the thickness after drying.
It is applied so as to be in the range of m.

The magnetic layer coated on the non-magnetic support is usually dried after the treatment for orienting the ferromagnetic powder in the magnetic layer, that is, the magnetic field orientation treatment. If necessary, surface smoothing treatment is performed. The magnetic recording medium that has been subjected to surface smoothing treatment is then cut into a desired shape.

Next, examples and comparative examples of the present invention will be shown. The indication "part" in the examples and comparative examples means "part by weight".

Example 1 The following composition was kneaded and dispersed for 48 hours using a ball mill, 14 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added thereto, and the mixture was further kneaded and dispersed for 1 hour, and then 1 μm. A magnetic paint was prepared by filtering with a filter having an average pore size of. The thickness of the obtained magnetic paint is 30 μm so that the thickness of the magnetic layer after drying is 8.0 μm.
It was coated on the surface of the polyethylene terephthalate support of Example 1 using a reverse roll.

Magnetic coating composition Co-containing γ-Fe ₂ O ₃ powder 100 parts (Nitrogen adsorption specific surface area: 50 m ² / g) Vinyl chloride / vinyl acetate copolymer 13 parts (VMCH, Union Carbide Co.) Polycarbonate polyurethane A 10 parts Phenoxy resin 4 parts (PKHH, manufactured by Union Carbide) Carbon black (average particle size: 120 mμ) 10 parts α-Al ₂ O ₃ (average particle size: 0.38 μm) 1 part Lecithin 3 parts Butyl stearate 1 part Methyl ethyl ketone 60 parts Toluene 80 Parts Tetrahydrofuran 60 parts However, the above polycarbonate polyurethane A is obtained from 8 parts by mole of hexanediol as a polyhydric alcohol component and 1 part by mole of 4,4′-diphenylmethane diisocyanate as a polyisocyanate component, and has a number average molecular weight of 30,000 and Tg. Is -17 ° C.

The non-magnetic support coated with the magnetic paint is subjected to magnetic field orientation treatment with a 3000 gauss magnet while the magnetic paint is undried.
After further drying, after performing a super calendar treatment,
A memory tape was manufactured by slitting a width of 1/2 inch.

[Example 2] 14 parts of the polyisocyanate and 13 parts of the vinyl chloride / vinyl acetate copolymer used in Example 1 were used, respectively.
A memory tape was manufactured in the same manner as in Example 1 except that 15 parts of polycarbonate polyurethane B having the following constitution was used instead of 10 parts of polycarbonate polyurethane A used in Example 1.

Polycarbonate polyurethane B is obtained from 6 parts by mole of hexanediol as a polyhydric alcohol component and 1 part by mole of 4,4'-diphenylmethane diisocyanate as a polyisocyanate component, and has a number average molecular weight of 100,00.
0, Tg is -5 ° C.

Example 3 A memory tape was produced in the same manner as in Example 2 except that the polycarbonate polyurethane C used in Example 2 was replaced with the polycarbonate polyurethane C having the following structure.

Polycarbonate polyurethane C is obtained from 2 parts by mole of hexanediol as a polyhydric alcohol component and 1 part by mole of 4-4'-diphenylmethane diisocyanate as a polyisocyanate component, and has a number average molecular weight of 50,00.
0, Tg is + 15 ℃.

Example 4 A memory tape was manufactured in the same manner as in Example 2 except that the polycarbonate polyurethane B used in Example 2 was replaced by the polycarbonate polyurethane D having the following structure.

Polycarbonate polyurethane D is obtained from 3 parts by mole of hexanediol as a polyhydric alcohol component, 2 parts by mole of cyclohexanedimethanol and 1 part by mole of 4,4′-diphenylmethane diisocyanate as a polyisocyanate component, and has a number average molecular weight of 30,000 and a Tg of Tg. It is + 30 ° C.

[Comparative Example 1] A memory tape was manufactured in the same manner as in Example 2 except that the polyester polyurethane E having the following constitution was used in place of the polycarbonate polyurethane B used in Example 2.

Polyester polyurethane E comprises 6 parts by mass of butanediol as a polyhydric alcohol component, 5 parts by mol of adipic acid as a polybasic acid component, and 4 parts as a polyisocyanate component.
It is obtained from 1 part by mole of 4'-diphenylmethane diisocyanate and has a number average molecular weight of 120,000 and a Tg of -25 ° C.

Comparative Example 2 A memory tape was manufactured in the same manner as in Example 2 except that the polycarbonate polyurethane A used in Example 1 was used instead of the polycarbonate polyurethane B used in Example 2.

The physical properties of the memory tape obtained as described above were evaluated by the following methods.

[Evaluation Method] Glossiness of magnetic layer surface According to JISZ 8741, refractive index is 1.567 at an incident angle of 45 degrees.
The specular gloss of the glass surface was measured as 100%.

Reproduction output A magnetic tape unit F-613 manufactured by Fujitsu Ltd. was equipped with a permalloy head, and the output of 6250 BPI was measured at a running speed of 5.0 m / sec to obtain the relative output with respect to the NBS (National Bureau of Standard) tape. .

Coefficient of friction The tension required when a stainless steel pole with a diameter of 24 mm is wrapped around a magnetic surface and contacted at an angle of 180 degrees while applying 65 g (T ₁ ) of tension and rotating the stainless pole at 63 rpm (T ₂ ). Was measured. Then, the friction coefficient μ was calculated by the formula of μ = 1 / π · lnT ₂ / T ₁ .

Friction coefficient after long-term storage The above-mentioned friction coefficient was measured for a tape that had been stored for 3 months under the conditions of a temperature of 60 ° C. and a humidity of 80% RH.

Adhesiveness After a lapse of 7 days in an atmosphere of a temperature of 60 ° C. and a humidity of 80% RH, a magnetic tape device F-613 manufactured by Fujitsu Ltd. was used with a Permalloy head to make the total tape length (2400 feet) 5.0 m /
Run in the feed direction at a running speed of 2 seconds and then rewind at 15 m / s. After repeating this 5 times, BOT (Beg
Gining of Tape, tape running start position) The tape was stopped and the sticky substance adhering to the tape surface at the running stop was visually observed. The dirt condition was evaluated from AA to EE according to the following evaluation criteria from good to bad.

AA: No sticky material. BB: There are some sticky substances.

CC: A little sticky. DD: There are quite a lot of stickies.

EE: There are many sticky substances.

Soluble fraction Peel off the magnetic layer from the obtained tape and put 3g in a beaker.
N-hexane (200 ml) was added to the peeled magnetic layer and heated and stirred at 60 ° C., and butyl stearate added as a lubricant was extracted and removed. 200 ml of tetrahydrofuran purified by distillation was added to the magnetic layer from which the lubricant had been removed, and the mixture was heated and stirred at 60 ° C. for 1 hour and then extracted, and the solvent of the extract was removed to obtain a tetrahydrofuran-soluble component of the binder. Then, the ratio of the tetrahydrofuran-soluble component of the binder to the total binder in the magnetic layer was determined.

The total amount of the binder (total binder) was determined by measuring the organic matter content in the magnetic layer by a thermobalance method and subtracting the hexane extracted content from the organic matter content.

The binder composition of each of the above examples is shown in Table 1, and the measurement results of its physical properties are shown in Table 2.

As is clear from Table 2, the soluble fraction of tetrahydrofuran according to the present invention is low, and the magnetic recording media containing polycarbonate polyurethane (Examples 1 to 4) have a low friction coefficient and a small amount of sticky matter attached. Furthermore, since the friction coefficient after long-term storage is low, it is particularly excellent in running durability and running durability after long-term storage. In addition, Example 1 considered to have a high polyisocyanate component and a high crosslink density
In addition, since the reproduction output is also high, it can be seen that the electromagnetic conversion characteristics are excellent.

Claims (4)

[Claims] 1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing a ferromagnetic powder dispersed in the binder on the support, wherein the binder contains polycarbonate polyurethane, and a curing treatment is performed. A magnetic recording medium characterized in that the binder has a soluble fraction of 35% by weight or less after extraction with tetrahydrofuran at 60 ° C. 2. The magnetic recording medium according to claim 1, wherein the soluble content is 25% by weight or less. 3. The magnetic recording medium according to claim 1, wherein the polycarbonate polyurethane is contained in an amount of 20 to 90% by weight in the total binder. 4. The magnetic recording according to claim 1, wherein the polycarbonate polyurethane is a polymer obtained from a polycarbonate polyol having a hydroxyl group at a terminal, a chain extender and an organic diisocyanate compound by a polymerization reaction. Medium.