JP2579501B2 - Polyurethane resin for magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyurethane resin for a magnetic recording medium.

[Conventional technology]

The magnetic recording medium is manufactured by applying a magnetic paint comprising a magnetic powder, a binder, an organic solvent, and other additives as necessary onto a non-magnetic substrate such as a polyester film and drying.

The magnetic recording medium has a high reproduction output, and in order to obtain electrical characteristics such as a high S / N ratio, the magnetic powder in the paint is uniformly dispersed, the magnetic coating surface is smooth, and the obtained Various properties such as excellent durability of the magnetic recording medium are required.

Therefore, various binders have been studied to satisfy these properties.

On the other hand, the saturation magnetization Bm and the remanence
For the purpose of increasing the Br ratio Br / Bm (square ratio) and lowering the porosity, a magnetic recording medium using a polyurethane resin into which a component containing a metal sulfonate is introduced as a binder has been proposed. Publication No. 58-41565).

[Problems to be solved by the invention]

However, the magnetic recording medium obtained in Japanese Patent Publication No. 58-41565 has the drawback that the durability is insufficient due to the problem of hydrolysis resistance, and that the thixotropic property of the obtained magnetic paint is increased. Was.

The present invention relates to a coating material for a magnetic recording medium using a novel polyurethane resin as a binder, wherein the magnetic powder in the coating material is uniformly dispersed, the surface of the magnetic coating film is smooth, and the obtained magnetic recording It is an object of the present invention to provide a polyurethane resin for a magnetic recording medium having various properties such as excellent durability of a medium and low thixotropic property of the obtained paint.

[Means for solving the problem]

That is, the present invention provides a polycaprolactone diol obtained by polymerizing ε-caprolactone using a dihydroxy compound having a benzene ring as a skeleton and having one or two metal sulfonate groups as an initiator, and a diisocyanate as an inert solvent. SUMMARY OF THE INVENTION The gist of the present invention is a method for producing a polyurethane resin for a magnetic recording medium, which is characterized in that solution polymerization is carried out therein.

In the present invention, in the polymerization of ε-caprolactone, a dihydroxy compound having a benzene ring as a skeleton and one or two sulfonic acid metal bases is used as an initiator, and the ratio of the polymerization initiator and ε-caprolactone used is Examples thereof include a molar ratio of 1: 2 to 1:50 (polymerization initiator: ε-caprolactone), preferably a range of 1: 4 to 1:20. When the molar ratio of the polymerization initiator to ε-caprolactone is more than 1: 2, the resulting polycaprolactone dihydroxy compound has poor solubility in a solvent and lacks practicality.

It has a benzene ring as a skeleton and is used as a polymerization initiator.
Examples of the dihydroxy compound having one or two metal sulfonate groups include a dihydroxy compound represented by the following general formula.

(In the above formula, α = 1 or 2, l = 1 to 8; m and n = 1 to 5; R represents X represents -O- or -COO-, and M represents Li, Na or K. Preferably, dihydroxy compounds represented by the following formulas (I) to (V) can be mentioned.

(In the formulas (I) to (V), M represents Na or K.) Of the compounds represented by the formulas (I) to (V), preferably, the compounds represented by the formulas (I) and (III) The compounds represented can be mentioned. In addition, their ethylene glycol solutions can also be used.

The polycaprolactone dihydroxy compound can be obtained by subjecting ε-caprolactone to ring-opening polymerization using the dihydroxy compound as a polymerization initiator according to a known method.

At the time of the reaction, a catalyst can be used if necessary.
The reaction temperature ranges from 50 to 300 ° C, preferably from 130 to 230 ° C.

Examples of the catalyst include alkali metal and organometallic compounds. As the alkali metal, lithium,
Sodium, potassium, etc., as organometallic compounds,
Organic titanium compounds such as tetrabutyl titanate and tetrapropyl titanate, dibutyltin oxide,
Organic tin compounds such as tin are exemplified.

Among them, an organic titanium compound is most preferable because it has a high catalytic activity and a product with little coloring can be obtained in a short time.

The content of the sulfonic acid metal base in the polyurethane resin of the present invention is determined by the content of the polycaprolactone diol, and is in the range of 2 to 150 μeq / g, preferably 2 to 10 μeq / g in the resin. .

If the sulfonic acid metal base content in the resin is less than 2 μeq / g, the effect on improving the dispersibility of the magnetic powder is small, and
When the ratio exceeds the above range, the thixotropic property of the obtained magnetic paint is remarkably increased, and the dispersibility of the magnetic powder is reduced. Further, many adverse effects such as a decrease in the hydrolysis resistance of the resin due to an increase in hydrophilicity occur.

In the present invention, it is necessary to include the above-mentioned polycaprolactone dihydroxy compound as the polyhydroxy compound having two or more active hydrogens in the molecule, but other polyhydroxy compounds can be used in combination. As such other polyhydroxy compounds, those having a molecular weight of 50 to 10,000 are generally used, and known polyhydroxy compounds generally used for polyurethane resin production, for example, low-molecular glycols, polyethers, polyesters, Examples thereof include polythioethers, polybutadiene glycols, silicon-containing polyols, and phosphorus-containing polyols.

As low molecular weight glycols, ethylene glycol,
Diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, 2-ethyl-1,3-hexanediol, N
-Alkyldiethanolamine, bisphenol A and the like. Further, a diol having a carboxyl group such as dimethylolpropionic acid or a low-molecular-weight polyol such as trimethylolpropane may be partially mixed and used.

Examples of the polyethers include polymerization products such as ethylene oxide, propylene oxide, and tetrahydrofuran, and copolymers. Polyethers obtained by condensation of the low-molecular glycols or 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 the polythioethers, it is particularly preferable to use thioglycol alone or a condensation product thereof with other glycols.

Examples of the polyesters include polyesters obtained by a dehydration condensation reaction from low-molecular glycols and dibasic acids, and lactone polyols obtained by ring-opening polymerization of lactone such as ε-caprolactone in the presence of the low-molecular glycol and the like. .

It is also possible to use a mixture of polyols having a trifunctional or higher function as the polyhydroxy compound.

Examples of the polyisocyanate compound used for producing a polyurethane resin by reacting with the polyhydroxy compound in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4'-diphenylmethane diisodianate. , Naphthalene-1,5-diisocyanate, tolidine diisocyanate, xylylene diisocyanate, isophorone diisodianate, hexamethylene diisocyanate, lysine ethyl ester diisocyanate, 4,4'-methylene bis (cyclohexyl isocyanate), ω, ω'-diisocyanate dimethylcyclohexane And the like, and adducts of these organic diisocyanate compounds with polyhydric alcohols.

Among these organic diisocyanates, good results are obtained in the case of a urethane resin using an organic diisocyanate containing a diisocyanate having a cyclohexyl group. The dispersibility and the surface smoothness of the magnetic layer are particularly excellent.

Chain extenders used in the production of polyurethane resins include ethylene glycol, propylene glycol, 1,4
-Glycols such as butanediol, 1,6-hexanediol, neopentyl glycol, 3-methyl-1,5-pentanediol and 1,5-pentanediol, low molecular weight polyols such as trimethylolpropane and glycerin, ethylenediamine, propylene Diamines such as diamine, hydrazine, piperazine and isophorone diamine can be mentioned.

It is also possible to use the above-mentioned polyhydroxy compounds as chain extenders.

In the present invention, the reaction for producing a polyurethane resin is a solution polymerization reaction. Solvents for solution polymerization include ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone which are generally inert to isocyanate groups, esters such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as toluene and benzene, and tetrahydrofuran. Can be mentioned.

The polyurethane resin is produced according to a conventional method, and examples of the catalyst at this time include tin-based, iron-based, and tertiary amine-based catalysts which are ordinary urethanization reaction catalysts. As a tin catalyst, dibutyltin dilaurate,
Dioctyltin dilaurate, dibutyltin dioctoate, stannas octoate, and the like. Examples of the iron-based catalyst include iron acetylacetonate and ferric chloride. Triethylamine as a tertiary nitrogen catalyst,
Triethylenediamine is exemplified.

In the present invention, the method for producing a polyurethane resin is appropriately selected from known production methods in consideration of the degree of polymerization of the target polyurethane resin, the type of raw materials to be used, and the like. For example, usually a solvent inert to the isocyanate group is used, and if necessary, a normal urethanization catalyst is used.
Reacting a polyhydroxy compound having active hydrogen with a stoichiometric excess of a polyisocyanate compound in a temperature range of 10 to 150 ° C., preferably 20 to 130 ° C. to produce a prepolymer having terminal isocyanate groups, A method of obtaining a polyurethane resin containing a hydroxyl group at a terminal by reacting a diol, a diamine, a triol, or the like which is a chain extender,
Alternatively, a method in which a polyhydroxy compound, a chain extender and a polyisocyanate compound are simultaneously reacted at a stoichiometrically charged amount in which a hydroxyl group becomes excessive to obtain a polyurethane resin having a terminal hydroxyl group can be used. Also, a method of reacting a polyisocyanate compound with a polyhydroxy compound without using a chain extender to obtain a polyurethane resin having a terminal hydroxyl group, and further reacting a polyhydroxy compound with a polyisocyanate compound to obtain a terminal hydroxyl group, and further producing a polyisocyanate A method of reacting a compound to obtain a polyurethane resin having a terminal hydroxyl group can also be employed.

The weight average molecular weight of the polyurethane resin of the present invention thus obtained is from 5,000 to 200,000, preferably from 10,000 to
In the range of 150,000. If the weight average molecular weight is less than 5,000, the mechanical properties of the polyurethane resin are inferior, and the durability of the magnetic recording medium deteriorates. If it is larger than 200,000, the dispersibility of the magnetic powder is poor, and the surface smoothness of the magnetic recording medium is poor.

The magnetic layer of the magnetic recording medium is kneaded with a binder, a magnetic powder, and, if necessary, each component added with a suitable organic solvent.
It is formed by preparing a magnetic paint, applying it to the surface of the non-magnetic support, and then drying it.

As the binder, in addition to the polyurethane resin obtained in the present invention, a low molecular weight polyisocyanate compound as a cross-linking agent, a vinyl chloride-vinyl acetate copolymer used as a normal binder component, nitrocellulose, an epoxy resin, a phenoxy resin It is also possible to use a mixture of a thermoplastic polyurethane resin and the like. Also, it can be used in combination with another polar group-containing binder.

As the low molecular weight polyisocyanate compound, adducts of isocyanate compounds having two or more isocyanate groups (adducts with dihydric or trihydric polyhydric alcohols, adducts such as dimers, trimers, etc., Adduct, etc.) can be used.

Examples of such a low molecular weight polyisocyanate compound include Bayer's trade names Desmodule L and Desmodule N, Nippon Polyurethane Industry Co., Ltd.
Trade names such as Coronate L and Coronate HL, Mitech GP105A manufactured by Mitsubishi Kasei Kogyo Co., Ltd., and Mytec NY218A (registered trademark manufactured by Mitsubishi Kasei Kogyo Co., Ltd.).

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

As the magnetic powder used in the magnetic recording medium of the present invention,
It is a known substance conventionally used, for example, γ
-Iron oxide, cobalt coated γ-iron oxide, cobalt doped γ
- iron oxide, CrO _2, barium ferrite, magnetic alloy powder, and a metal magnetic powder and the like.

When forming the magnetic layer of the magnetic recording medium, if necessary, various commonly used additives such as an antistatic agent, carbon black, a lubricant, and a non-magnetic inorganic pigment may be used. You can also.

As the non-magnetic support, polyester (for example, polyethylene terephthalate), polyamide, polyolefin, cellulose derivative, non-magnetic metal, paper and the like are used, and the shapes thereof are films, tapes, sheets, cards,
Disk and the like.

By incorporating the polyurethane resin of the present invention thus obtained into a binder for a magnetic recording medium, the dispersibility of the magnetic powder is much higher than that of a conventional thermoplastic polyurethane resin, and the magnetic coating is performed. A magnetic recording medium having excellent surface smoothness of the film, excellent resistance to wet heat and durability, can be obtained.

In addition, compared to a polyurethane resin obtained using a conventional sulfonic acid metal base-containing polycondensation polyester glycol, it is easier to introduce a sulfonic acid metal base,
One or two sulfonic acid metal bases are selectively introduced into one molecule of the polycaprolactone dihydroxy compound, and a plurality of sulfonic acid metal bases hardly enter into the resulting polyurethane molecular chain. The binder containing the resin has a small increase in the thixotropic property of the magnetic paint due to the interaction of the metal sulfonic acid salts that are not involved in the adsorption to the magnetic powder, and the effectiveness of the introduced metal sulfonic acid base is high and the amount to be introduced is small. Since it can be minimized,
It has many advantages, such as being able to suppress a decrease in wet heat resistance due to an increase in hydrophilicity.

〔Example〕

Next, the present invention will be described more specifically with reference to Examples.
The present invention is not limited to the following examples.

Examples 1 to 6, Comparative Examples 1 to 4 (1) Production of polycaprolactone diol 200 g of ε-caprolactone and 5 in a four-necked flask equipped with a thermometer, a stirrer, a condenser with a drying tube, and a nitrogen inlet tube.
-Sulfoisophthalic acid di-2-hydroxyethyl sodium salt <Compound (I), M = Na> 110.6 g, tetrabutyl titanate 31 mg were added, and the internal temperature was maintained at 150 ° C. for 10 hours to obtain polycaprolactone diol (a). I got The resulting polycaprolactone diol (a) has a hydroxyl value of 11
2.The content of sodium sulfonate base is 1,000μeq / g
Met.

In a similar manner, polycaprolactone diol (b) was produced using compound (III) (M = Na).

(2) Production of polyurethane resin 100 g of 4,4'-diphenylmethane diisocyanate, 284 g of cyclohexanone and 284 g of methyl ethyl ketone were charged into a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube, and the internal temperature was raised to 80 ° C. And stirred.
To this, 0.95 g of the polycaprolactone diol (a) obtained in the above (1) and 265.7 g of a commercially available polybutylene adipate having a number average molecular weight of 1,000 (N-4009: manufactured by Nippon Polyurethane)
Was added dropwise. After completion of the dropwise addition, a heating reaction was carried out at 80 ° C. for 2 hours to synthesize a prepolymer having a terminal isocyanate group. The prepolymer was subsequently treated with 1,4-butanediol 1
It was dropped into 2.6 g. After completion of the dropwise addition, a heating reaction was performed at 90 ° C. for 6 hours to obtain a polyurethane resin (A). Completion of the reaction was confirmed by the disappearance of the isocyanate group absorption at 2250 cm ^{-1 in} the infrared absorption spectrum. Further, the content of the sodium sulfonate group in the obtained polyurethane resin was 2.5 μeq / g.

Using the same solution polymerization method as the polyurethane resin (A),
From the raw materials shown in Table 1, polyurethane resin (B)
(F), and as a comparative example, a polyurethane resin (G),
(H) was obtained.

Further, as a comparative example, the same raw material as in Example 1 was used,
Polyurethane resin (A ') was produced according to the following bulk polymerization method, and Comparative Example 3 was obtained.

0.95 parts of polycaprolactone diol (number average molecular weight 1000) obtained by polymerizing ε-caprolactone using sodium 5-sulfoisophthalate di-2-hydroxyethyl salt <Compound (I), M = Na> as a polymerization initiator; 265.7 parts of polybutylene sipipete (N-4409, manufactured by Nippon Polyurethane, number average molecular weight 1000) and 1,4-butanediol 12.6
After heating each part to 110 ° C. to dissolve it, dehydration treatment was carried out under reduced pressure and vacuum for 1 hour. Then, at normal pressure, at 60 ° C
4,4'-diphenylmethane diisocyanate (MDI) 100
Was added and mixed well for 30 minutes.

Pour this mixture into a vat heated to 120 ° C,
After being left for about 5 hours, the mixture was further cured in a heating furnace at 100 ° C. for 3 days to complete the reaction.

It was taken out of the vat at room temperature, crushed, and dissolved in 284 parts of cyclohexanone and 284 parts of methyl ethyl ketone to obtain a polyurethane resin (A ').

Further, a polyurethane resin (B ′) was produced using the same raw materials of Example 2 according to the same bulk polymerization method, and Comparative Example 4 was obtained.

1) 4,4'-diphenylmethane diisocyanate 2) A mixture of 2,4-tolylene diisocyanate / 2,6-tolylene diisocyanate = 8/2 3) Inephorone diisocyanate 4) N-400g (Nippon Polyurethane, number average molecular weight) 100
0) 5) PLC-208 (manufactured by Daicel Chemical Industries, number average molecular weight 850) Polycaprolactone polyol using ethylene glycol as a polymerization initiator 6) Polycaprolactone polyol having number average molecular weight 800 using β-hydroxyethyl terephthalate as a polymerization initiator 7) Polycaprolactone diol having a number average molecular weight of 1000 using compound (I) <M = Na> as a polymerization initiator 8) polycaprolactone diol having a number average molecular weight 800 using compound (III) <M = K> as a polymerization initiator 9) Polyester diol having a number average molecular weight of 1000 obtained from sodium 5-sulfoisophthalate, adipic acid and 1,4-BG (sodium sulfonate base content = 10
(A) Evaluation of dispersibility of magnetic powder and thixotropic property of magnetic paint ○ Composition of magnetic paint 100 parts of polyurethane resin (resin solid content 40%) 120 parts of Co-containing γ-Fe ₂ O ₃ 100 parts of cyclohexanone 100 parts of methyl isobutyl 100 parts of ketone 200 parts of methyl ethyl ketone A mixture of the above composition was kneaded for 10 hours by a paint shaker, and the obtained magnetic paint was applied on a polyethylene terephthalate film so that the film thickness after drying became 30 μm. It was removed with a dryer. The surface gloss of the obtained magnetic coating film was measured to evaluate dispersibility.

Further, the thixotropic property of the obtained magnetic paint was measured using a rotational viscometer. Table 2 shows the results.

From the results in Table 2, the polyurethane resin (A) of the example was obtained.
It can be said that the magnetic coating film using (F) has an averagely high surface gloss and is excellent in dispersibility of the magnetic powder. Also, the structural viscosity of the magnetic paint is low.

(B) Evaluation of wet heat resistance Polyurethane resins (A) to (H) and (A ′),
100 parts of the solution of (B ′) was mixed with a low molecular weight polyisocyanate Mytec AD75 (manufactured by Mitsubishi Kasei Kogyo Co., Ltd .: T
A solution obtained by adding 5.3 parts of a reaction product of DI and trimethylolpropane (trademark of Mytec Co., Ltd.) was applied so that the film thickness after drying was about 100 μm, and allowed to stand at room temperature for 30 minutes.
Initial mechanical properties of the film obtained by curing over time and
The mechanical properties were measured after two weeks under the moist heat condition of 80 ° C. and 95% relative humidity, and the moist heat resistance was evaluated from the strength and the retention of elongation.

From the results in Table 3, the polyurethane resin (A) of the example was obtained.
~ (F) shows that it is excellent in moist heat resistance.

(C) Evaluation of durability Polyurethane resins (A) to (H) and (A ′),
The durability was evaluated using a floppy disk manufactured using (B ′).

○ Composition of magnetic paint Polyurethane resin 100 parts (resin solid content 40%) Vinyl chloride-vinyl acetate copolymer 40 parts (VAGH, manufactured by UCC) Co-containing γ-Fe ₂ O ₃ 180 parts Lecithin 3 parts Carbon black 5 parts Lubricant 2 parts Methyl ethyl ketone 135 parts Methyl isobutyl ketone 135 parts Cyclohexanone 135 parts After kneading the mixture of the above composition in a sand grind mill for 6 hours, 15 parts of Mitec AD75 are mixed as a crosslinking agent, and the obtained magnetic paint is mixed. It was applied so that the film thickness after drying on a 75 μm-thick polyethylene terephthalate film was 2 μm, and after curing, was punched out into a floppy disk of a predetermined size. The obtained floppy disk was mounted on a drive with a load of 100 g applied to the head, and the time required for the initial output to drop to 60% or less under conditions of a temperature of 40 ° C and a relative humidity of 80% was measured. As a guide. At the same time, the initial S / N ratio was measured.

 Table 4 shows the results.

From the results in Table 4, the polyurethane resin (A) of the example was obtained.
It can be seen that the magnetic recording media manufactured using (F) to (F) have excellent durability.

〔The invention's effect〕

A magnetic recording medium using the polyurethane resin of the present invention as a binder has a high dispersibility of magnetic powder, excellent surface smoothness of a magnetic coating film, and excellent effects of wet heat resistance and durability.

Claims (1)

(57) [Claims] A polycaprolactone diol obtained by polymerizing ε-caprolactone using a dihydroxy compound having a benzene ring as a skeleton and having one or two metal sulfonate groups as an initiator, and a diisocyanate in an inert solvent. A method for producing a polyurethane resin for a magnetic recording medium, comprising performing a solution polymerization in step (a).