JPH0658736B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more specifically, it has good dispersibility of magnetic particles in a magnetic coating layer, and has good surface smoothness and durability. The present invention relates to an improved urethane resin-containing binder for providing an excellent magnetic recording medium.

[Prior art]

Generally, a magnetic recording medium is manufactured by coating a magnetic coating material comprising a magnetic powder, a binder, an organic solvent and, if necessary, other additives on a non-magnetic support such as a polyester film and drying.

In order to obtain excellent electrical characteristics such as high reproduction output and high SN ratio, the magnetic recording medium as a binder has a uniform dispersibility of magnetic particles in the magnetic coating and a high degree of smoothness on the surface of the magnetic coating. And the durability is required.

Vinyl chloride-vinyl acetate-polyvinyl alcohol copolymers, linear polyurethane resins, etc. are widely used as binders having these relatively good characteristics, but each has its advantages and disadvantages and is still insufficient as a binder for magnetic recording media. I can't say that.

Conventionally used linear polyurethane resins are obtained by reacting a long-chain polyol having hydroxyl groups at both ends with an organic diisocyanate and a diamine, a diol or the like, which is a chain extender having two active hydrogens of relatively low molecular weight. Polyester polyols or polyether polyols are mainly used as such long-chain polyesters having hydroxyl groups at both ends.

Such polyester polyols are generally ethylene glycol or 1,4-butylene glycol, 1,6-
Examples include polyesters synthesized from hexane glycol and the like and adipic acid, and examples of the polyether-based polyols include polymers or copolymers of ethylene oxide and propylene oxide, and polytetramethylene ether glycol which is a polymer of tetrahydrofuran. It is used.

[Problems to be Solved by the Present Invention]

However, it cannot be said that the urethane resin using these polyols has sufficient dispersibility of the magnetic powder and the surface smoothness of the magnetic coating film, and in the case of the polyurethane resin using the above polyester polyol, the water resistance and the moisture resistance are high. The heat resistance is poor, and on the other hand, the polyurethane resin using a polyether polyol has a drawback that it is apt to be oxidatively deteriorated and has poor heat resistance because it contains an ether bond.

[Means for Solving the Problems]

The present inventors have conducted various studies in view of the present situation, and as a result, have opened ε-caprolactone using glycols having an aromatic ring as a compound having two or more active hydrogens in the molecule as a polymerization initiator. A compound containing a polycaprolactone polyol having an average molecular weight of 250 to 10,000 obtained by ring polymerization is used, and a polyurethane resin obtained by reacting this with an organic diisocyanate and a low molecular weight polyisocyanate compound are contained in a binder. Then, it was found that a magnetic recording medium having much more excellent surface smoothness, dispersibility of magnetic powder, water resistance, and heat and humidity resistance can be obtained as compared with a conventional linear polyurethane. Achieved

The present invention will be described in more detail below.

The polycaprolactone polyol used in the present invention is
According to a method known per se, ε-caprolactone is obtained by ring-opening polymerization in the presence of a catalyst, using a glycol having an aromatic ring as an initiator.

Examples of the aromatic ring-containing glycols used as the polymerization initiator include bisphenol A, hydroquinone bis (2-hydroxyethyl ether), p-xylylene glycol, bis (β-hydroxyethyl) terephthalate, and ethylene glycol in these glycols, Glycols having an aromatic ring such as a polymerization product or a copolymerization product to which propylene oxide or butylene oxide tetrahydrofuran is added can be used.

By using a glycol containing an aromatic ring as a polymerization disclosure agent, a magnetic recording medium having particularly excellent durability can be obtained.

The polycaprolactone polyol used in the present invention has a weight average molecular weight of 250 to 10,000, preferably 250 to 10,000.
It has 3,000.

In addition, these polycaprolactone polyols may be used alone or as a mixture of several kinds of polycaprolactone polyols.

In the present invention, it is necessary to contain the above polycarlolactone polyol as a compound having two or more active hydrogens in the molecule, but other compounds having active hydrogens can be used in combination. A compound having two or more active hydrogens in the molecule usually has a molecular weight of 5
A known polyhydroxy compound generally having 0 to 10000 and used for producing polyurethane, for example, low molecular glycols, polyethers, polyesters, polyacetals, polythioethers,
Polybutadiene glycols, silicon-containing polyols,
A phosphorus-containing polyol or the like can be used.

The low molecular weight glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, pentaethylene glycol, hexamethylene glycol, neopentyl glycol, and 2 -Ethyl-1,3-hexanediol, N-alkyldiethanolamine, bisphenol A, etc. are used. Furthermore, it is possible to partially mix and use diols having a carboxyl group such as dimethylolpropionic acid.

Examples of polyethers include polymerization products or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran and the like. Further, polyethers obtained by condensation of the low molecular glycols, mixed ethers, and products obtained by addition-polymerizing ethylene oxide and propylene oxide to these polyethers and the low molecular glycol can also be used.

As polythioethers, it is particularly preferable to use thioglycol alone or a condensation product of thioglycol with other glycols.

Examples of the polyacetals include water-insoluble type polyacetals obtained from 1,4-butanediol and formaldehyde or from 4,4'-dioxyethoxydiphenyldimethylmethane and formaldehyde.

Typical examples of the polyesters are polyesters obtained by a dehydration condensation reaction from low molecular weight glycols and a dibasic acid.

It is also possible to partially use a trifunctional or higher functional polyol in the polyhydroxy compound.

In the present invention, it is desirable that the polycaprolactone polyol content is at least 10% with respect to the total amount of the compound having two or more active hydrogens, and the use amount of the polycaprolactone polyol is 10 wt% or less. It is not preferable because the dispersibility of the magnetic powder and the surface smoothness of the magnetic coating film cannot be sufficiently expressed.

The organic diisocyanate used for producing a polyurethane resin by reacting with a compound having two or more active hydrogens in the molecule in the present invention includes 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate. Isocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene-1,5-
Diisocyanate, tolidine diisocyanate, xylylene diisocyanate, isophorone diisocyanate,
Hexamethylene diisocyanate, lysine ethyl ester diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), ω, ω′-diisocyanate dimethylcyclohexane and the like can be used.

Among these organic diisocyanates, good results were obtained in the case of a urethane resin using an organic diisocyanate containing a cyclohexyl group-containing diisocyanate, in particular, a diisocyanate containing isophorone diisocyanate. The urethane resin containing nato is particularly excellent in dispersibility of the magnetic powder and surface smoothness of the magnetic layer, and is a particularly preferred diisocyanate in the present invention. The content of isophorone diisocyanate in the diisocyanate is 20-
100 wt% is preferred.

The method for producing the polyurethane resin is appropriately selected from known production methods in consideration of the degree of polymerization of the desired polyureta, the type of raw material used, etc., but is usually a solvent inert to the isocyanate group, if necessary. 10 to 150 ° C. using an ordinary urethanization catalyst if necessary
A polyhydroxy compound having active hydrogen, preferably in a temperature range of 20 to 130 ° C., is reacted with a stoichiometric excess of an organic diisocyanate to produce a prepolymer having a terminal isocyanate group, and then shown below. To obtain a polyurethane resin having terminal hydroxyl groups by reacting a chain extender such as diol or diamine, or by reacting a stoichiometrically excess polyhydroxy compound with a chain extender and an organic diisocyanate at the same time. Examples thereof include a method of obtaining a polyurethane resin having a hydroxyl group. Further, a method of reacting a polyisocyanate and a polyhydroxy compound without using a chain extender to obtain a polyurethane resin having a terminal hydroxyl group, and further reacting a stoichiometrically excess polyhydroxy compound and an organic diisocyanate. A method of obtaining a polyurethane resin having a terminal hydroxyl group and further reacting it with an organic diisocyanate to obtain a polyurethane resin having a terminal hydroxyl group can also be adopted.

As chain extenders used for producing polyurethane resins, glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and pentanediol, bisphenol A, hydroquinone bis (2- Hydroxyethyl ether), p-xylylene glycol, bis (β-
Glycols having an aromatic ring such as (hydroxyethyl) phthalate, ethylenediamine, propylenediamine,
Diamines such as hydrazine, isophorone diamine, metaphenylenediamine, 4,4'-diaminodiphenylmethane, and 3,3'-dichloro-4,4'-diaminodiphenylmethane can be used.

In the present invention, the weight average molecular weight of these polyurethane resins is preferably 1,000 to 300,000.
In particular, a polyurea resin having a weight average molecular weight of 1,000 to 30,000 is excellent in the dispersibility of magnetic powder and the surface smoothness of a magnetic coating film. On the other hand, a magnetic layer using a polyurethane resin having a weight average molecular weight of 30,000 or more is excellent in film strength.

In order to obtain a polyurethane resin having a weight average molecular weight of 30,000 or more, a method of producing a prepolymer having a terminal isocyanate group and then performing a chain extension reaction using a chain extender is preferable.

The binder of the present invention contains a low molecular weight polyisocyanate compound as a curing agent together with the polyurethane resin, and such a low molecular weight polyisocyanate compound is an isocyanate compound having two or more isocyanate groups. Adduct (adduct with divalent or trivalent polyhydric alcohol, dimer, trimer, etc.,
Adduct with water, etc.) can be used.

Examples of such a low molecular weight polyisocyanate compound include trade names DESMODUL L, DESMODULN manufactured by Bayer Co., Coronate L manufactured by Nippon Polyurethane Industry Co., Coronate HL, manufactured by Mitsubishi Kasei Co., Ltd. Mitec GP105A, Mitec NY218A (registered trademark of Mitsubishi Kasei Co., Ltd.) and the like.

These low molecular weight polyisocyanate compounds are used in a proportion of 3 to 50 (weight)% of the total amount of the binder.

The binder used in the present invention includes the above polyurethane resin, a low molecular weight polyisocyanate compound, and a vinyl chloride-vinyl acetate-polyvinyl alcohol copolymer usually used as a binder component, nitrocellulose, an epoxy resin, and phenoxy. It is also possible to use a mixture of resins and the like. These binders are added to such an extent that the effect obtained by using the binder composed of the polyurethane resin and the low molecular weight polyisocyanate compound is not impaired, and usually 0 to 80% by weight based on the total amount of the binder. It is appropriately determined within the range.

The magnetic powder used in the magnetic recording medium of the present invention is a conventionally known magnetic powder, for example, γ-
Iron oxide, cobalt-coated γ-iron oxide, cobalt-doped γ-
Examples thereof include iron oxide, CrC ₂ , alloy magnetic powder, and metal magnetic powder.

Further, when forming the magnetic layer of the magnetic recording medium, various kinds of commonly used additives such as antistatic agents, carbon black, lubricants, non-magnetic inorganic pigments, etc. may be added and used, if necessary. You can also

As the non-magnetic support, polyester (for example, polyethylene terephthalate), polyamide, polyolefin, cellulose derivative, non-magnetic metal, paper or the like is used, and its shape is a film, tape, sheet, card,
For example, a disk.

The magnetic layer of the magnetic recording medium is prepared by kneading the binder of the present invention, the above-mentioned magnetic powder, and each component added as necessary with a known suitable solvent to prepare a magnetic coating material, and coating the surface of the support. It is formed by applying and then drying.

As the solvent, ketones such as methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, and aromatic hydrocarbon solvents such as toluene and benzene are used.

As described above, the magnetic recording medium according to the present invention is obtained by using a binder containing a specific polyurethane resin, and has a surface smoothness and a magnetic powder which are higher than those obtained by using a conventional linear polyurethane resin. Has good dispersibility and is also excellent in water resistance and wet heat resistance.

〔Example〕

Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

In the examples, "parts" represent parts by weight.

Example 1 (1) Production of Polyurethane Resin-1 A four-necked flask with an internal capacity of 1 equipped with a thermometer, a stirrer, a dropping funnel, a cooler with a drying tube, etc., had a molecular weight of 800 using paraxylylene glycol as an initiator. Polycaprolactone polyol 480g, methyl isobutyl ketone 59
1 g and 0.03 g of dibutyltin dilaurate were charged and the internal temperature was adjusted to 80 ° C. and the mixture was stirred. 111 g of isophorodiisocyanate was added dropwise to this. After completion of the dropping, a heating reaction was carried out at 80 ° C. for 6 hours to obtain a polyurethane resin.

(2) Production of magnetic recording medium Polyurethane resin-1 240 parts Vinyl chloride-vinyl acetate-polyvinyl alcohol copolymer 50 parts (1000GKT manufactured by Denki Kagaku Kogyo Co., Ltd.) Lecithin 10 parts Carbon black 40 parts Co-containing γ- Fe ₂ O ₃ 740 parts Methyl ethyl ketone 1440 parts Methyl isobutyl ketone 480 parts Cyclohexanone 480 parts After kneading the mixture of the above composition for 6 hours in a sand grind mill, 30 parts of Mitec GP105A (registered trademark of Mitsubishi Kasei Co., Ltd.) as a crosslinking agent Were mixed and filtered to obtain a magnetic paint. This magnetic paint was applied onto a polyethylene terephthalate film so that the film thickness after drying would be 5 μm and dried.

The results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium are shown in Table 1.

The film properties of polyurethane resin-1 are shown in Table 2.

Further, the above-mentioned magnetic paint was applied and punched out on a dried film 5 inch floppy disk, and an accelerated durability test was conducted as follows. The results are shown in Table 3.

Accelerated durability test method (1) Device: 5-inch floppy disk drive (TE
A modified SCOM) was used.

(2) Test environment: Temperature 40 ° C. Relative humidity 80% (3) Evaluation method: Heads are mounted at two locations on a floppy disk and a load of 100 g is applied to one head. The output is detected by the other head. The durability was evaluated from the time when the output of the initially written signal was 60% or less.

Comparative Example 1 (1) Production of Polyurethane Resin-2 In the same device as in Example 1, 97.5 g of 4,4'-diphenylmethane diisocyanate and 55 of methyl ethyl ketone were added.
5 g was charged, the internal temperature was adjusted to 70 ° C., and the mixture was stirred. Polycaprolactone polyol (trade name Praxel 20
5; Daicel Chemical Industries Ltd .: Bifunctional polycaprolactone polyol having a molecular weight of 550) (198 g) was added dropwise from a dropping funnel. After completion of the dropwise addition, a heating reaction was carried out at 70 ° C. for 2 hours to prepare a prepolymer having an isocyanate group at the end. Subsequently, 3.6 g of 1,4-butanediol was added to this reaction product.
And 0.03 g of dibutyltin dilaurate as a catalyst was added dropwise. After completion of the dropping, heating reaction was carried out at 70 ° C. for 5 hours. The end of the reaction is 225 in the infrared absorption spectrum.
This was confirmed by the disappearance of the absorption of the isocyanate group at 0 cm ^-1 .

(2) Production of magnetic recording medium Polyurethane resin-2 343 parts Nitrocellulose 150 parts (FM-200 manufactured by Asahi Kasei Corporation) Vinyl chloride-vinyl acetate-polyvinyl alcohol copolymer 50 parts (Electrochemical Industry Co., Ltd. ) 1000 GKT) Lecithin 10 parts Carbon black 40 parts Co-containing γ-Fe ₂ O ₃ 740 parts Methyl ethyl ketone 1440 parts Methyl isobutyl ketone 480 parts Cyclohexanone 480 parts After kneading the mixture of the above composition in a sand grind mill for 6 hours, a cross-linking agent As a mixture, 36 parts of Mitec GP105A (registered trademark of Mitsubishi Kasei Co .; Mitsubishi Kasei: TDI and trimethylolpropane reaction product) were mixed and filtered to obtain a magnetic coating material.

This magnetic paint was applied onto a polyethylene terephthalate film so that the film thickness after drying would be 5 μm, and dried.

The results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium are shown in Table 1, and the film properties of polyurethane resin-2 are shown in Table 2.

Comparative Example 2 (1) Production of Polyurethane Resin-3 A mixture of 80% 2,4-tolylene diisocyanate and 20% 2,6-tolylene diisocyanate in the same apparatus as in Example 1 (hereinafter referred to as 80-TDI). ) 66.1 g and methyl isobutyl ketone 500 g were charged, and the internal temperature was adjusted to 70
The mixture was brought to ℃ and stirred. Polyprolactone polyol (trade name: Praxel 208; manufactured by Daicel Chemical Industries, Ltd.):
Bifunctional polycaprolactone polyol with a molecular weight of 850)
150 g, 180 g of polytetramethylene ether glycol having a molecular weight of 1000 and 250 of methyl ethyl ketone
g mixture was added dropwise. After completion of the dropwise addition, a heating reaction was carried out at 70 ° C. for 2 hours to prepare a prepolymer having an isocyanate group at the end. Subsequently, 4.7 g of 1,6-hexanediol and 0.02 g of catalyst dibutyltin dilaurate were added dropwise to the reaction product. After the dropping was completed, a heating reaction was performed at 80 ° C. for 4 hours. The completion of the reaction was confirmed by the disappearance of the isocyanate group at 2250 cm ^{-1 in} the infrared absorption spectrum.

(2) Production of magnetic recording medium A magnetic coating material was prepared in the same manner as in (2) Production of magnetic recording medium of Comparative Example 1 except that polyurethane resin-3 was used instead of polyurethane resin-2, and the same procedure was followed. To produce a magnetic recording medium. The results of measuring the surface reflectance of the obtained magnetic coating film are shown in Table 1, and the film properties of polyurethane resin-3 are shown in Table 2.

Example 3 (1) Production of Polyurethane Resin-4 The same apparatus as in Example 1 was charged with 220 g of polycaprolactone polyol having a molecular weight of 800 and an initiator of dipropylene glycol and 264 g of methyl isobutyl ketone, and the internal temperature was adjusted to 80 ° C. And stirred. 80-TD to this
I43.5g was dripped. After completion of the dropping, a heating reaction was carried out at 80 ° C. for 4 hours to obtain a polyurethane resin.

(2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured in the same manner as in (2) Manufacturing of magnetic recording medium of Example 1 except that polyurethane resin-4 was used instead of polyurethane resin-1.

The results of measuring the surface reflectance of the obtained magnetic coating film are shown in Table 1, and the film properties of polyurethane resin-4 are shown in Table 2.

Further, an accelerated durability test was conducted in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 4 (1) Production of Polyurethane Resin-5 The same apparatus as in Example 1 was charged with 680 g of polycaprolactone polyol having a molecular weight of 850 as an initiator using neopentyl glycol as an initiator, 835 g of methyl isobutyl ketone and 0.08 g of dibutyltin dilaurate, Inner temperature 80 ℃
It was stirred at. Isophorone diisocyanate 15
5 g was added dropwise. After completion of the dropping, a heating reaction was carried out at 80 ° C. for 4 hours to obtain a polyurethane resin.

(2) Production of magnetic recording medium A magnetic recording medium was obtained in the same manner as in Example 1 except that polyurethane resin-5 was used instead of polyurethane resin-1 in Example 1.

The results of measuring the surface reflectance of the obtained magnetic coating film are shown in Table 1.

Further, an accelerated durability test was conducted in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 5 (1) Production of Polyurethane Resin-6 In a device similar to that of Example 1, 480 g of polycaprolactone polyol having a molecular weight of 800 and using 1,6-hexanediol initiator, 594 g of methyl isobutyl ketone and 0.06 g of dibutyltin dilaurate were used. Charge the internal temperature of 80 ℃
And stirred. Isophorone diisocyanate 8
9 g was added dropwise. After completion of the dropping, a heating reaction was performed at 80 ° C. for 3 hours. Subsequently, 25 g of 4,4'-diphenylmethane diisocyanate was added dropwise, and after completion of the addition, a heating reaction was carried out at 80 ° C for 2 hours to obtain a polyurethane resin.

(2) Production of magnetic recording medium A magnetic recording medium was obtained in the same manner as in Example 1 except that polyurethane resin-6 was used instead of polyurethane resin-1 in Example 1. The results of measuring the surface reflectance of the obtained magnetic coating film are shown in Table 1. Table 2 shows the film properties of the polyurethane resin-6.

Comparative Example 6 (1) Production of Polyurethane Resin-7 Instead of the polycaprolactone polyol (commercial name Praxel 205) of Comparative Example 1, polytetramethylene adipate (commercial name ODX-240: molecular weight 10 manufactured by Dainippon Ink and Chemicals, Inc.)
Polyurethane resin was produced in the same manner as in Comparative Example 1 except that 360 g of polytetramethylene adipate of No. 00 was used.

(2) Production of magnetic recording medium A magnetic recording medium was obtained in the same manner as in Comparative Example 1 except that polyurethane resin-7 was used instead of polyurethane resin-2 in Comparative Example 1.

The results of measuring the surface reflectance of the obtained coating film are shown in Table 1. In addition, Table 2 shows the film properties of the polyurethane resin-7.

Comparative Example 7 (1) Production of Polyurethane Resin-8 Polytetramethylene adipate (trade name ODX240) 2 in place of polycaprolactone polyol having a molecular weight of 800 using dipropylene glycol as an initiator in Comparative Example 3 2
A polyurethane resin was produced in the same manner as in Comparative Example 3 except that 75 g was used.

(2) Production of magnetic recording medium A magnetic recording medium was obtained in the same manner as in Example 1 except that polyurethane resin-8 was used instead of polyurethane resin-1 in Example 1.

The results of measuring the surface reflectance of the obtained magnetic coating film are shown in Table 1.
Table 2 shows the film physical properties of polyurethane resin-8.

Further, an accelerated durability test was conducted in the same manner as in Example 1. The results are shown in Table 3.

Claims (2)

[Claims] 1. A coating layer on a non-magnetic support contains a polyurethane resin obtained by reacting an organic diisocyanate with a compound having two or more active hydrogens in the molecule and a low molecular weight polyisocyanate compound. In a magnetic recording medium using a binder, a compound having two or more active hydrogens in the molecule is obtained by ring-opening polymerization of ε-caprolactone using a glycol having an aromatic ring as a polymerization initiator. A magnetic recording medium containing a polycaprolactone polyol having a weight average molecular weight of 250 to 10,000. 2. The magnetic material according to claim 1, wherein the compound having two or more active hydrogen atoms in the molecule contains at least 10% by weight of the polycaprolactone polyol. recoding media.