JPH06231444A - Polyurethane resin binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good surface smoothness and magnetic characteristics by using polyurethane resin having a specified compsn. of sulfonium salt structure in the molecule produced from long-chain polyols, chain-extending agent, and org. diisocyanate. CONSTITUTION:The binder consists of polyurethane resin having a sulfonium salt structure expressed by formula I in the molecule produced from long-chain polyols, chain-extending agent and org. diisocyanate. In formula I, A and B may be same or different urethane residues, and R and R' are same or different alkyl groups or aryl groups. Since polyurethane resin binder has the sulfonium structure, the magnetic recording medium using this resin has significantly improved surface smoothness and electromagnetic conversion characteristics compared to a conventional well-known medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyurethane resin binder for magnetic recording media such as magnetic tapes, magnetic disks and magnetic sheets. More specifically, the present invention relates to a polyurethane resin-based binder for obtaining a high-performance magnetic recording medium which is excellent in surface smoothness and magnetic properties of the magnetic layer of the magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media used for video and audio equipment, computers and the like have a magnetic material composed of magnetic particles and a binder resin on a non-magnetic support such as a polyester film typified by polyethylene terephthalate. It is obtained by forming layers. To form such a magnetic layer, magnetic particles are dispersed in a binder resin solution,
After that, it is obtained by coating on a non-magnetic support. Conventionally, as such a binder resin, a cellulosic resin, an epoxy resin, a vinyl resin, a polyester resin, a polyurethane resin, etc. have been used, but the dispersibility of the magnetic particles and the surface smoothness of the magnetic layer or It cannot be said that the electromagnetic conversion characteristics are sufficient. In particular, since such a binder resin has a weak interaction with magnetic particles, the dispersibility is poor and a smooth magnetic layer surface cannot be obtained.
Further, in recent years, as the recording density of the magnetic recording medium has been increased, the magnetic particles have been further made into fine particles, and the magnetic particles are strongly aggregated in the binder solution, making it more difficult to obtain a stable dispersion liquid. Therefore, conventionally, various dispersants have been used in order to stabilize the dispersion of the magnetic particles.

[0003]

However, in the binder resin and the dispersant as described above, the magnetic particles once dispersed are aggregated again with time due to the strong aggregating force of the magnetic particles, so that a stable magnetic recording medium is obtained. Has often been difficult to manufacture. Alternatively, since the conventionally used dispersant has a lower molecular weight than the binder resin, it bleeds to the surface of the magnetic layer, resulting in damage to the magnetic head. Therefore, there has been a strong demand for a binder resin that can obtain a stable dispersion liquid without using a dispersant. The present inventors have arrived at the present invention as a result of intensive studies in view of the above circumstances.

[0004]

[Means for Solving the Problems] That is, the present invention provides a polyurethane resin produced from a long-chain polyol, a chain-lengthening agent, and an organic diisocyanate, which has a sulfonium salt structure in its molecule, and is a polyurethane for a magnetic recording medium. It is a resin binder. The polyurethane resin in the present invention is typically represented by the following general formula [Chemical formula 1].

[0005]

(In the formula, A and B each represent a urethane residue which may be the same or different, and R and R
′ Represents an alkyl group or an aryl group, which may be the same as or different from each other. )

The method for producing the polyurethane resin according to the present invention is not limited, and can be obtained from a long-chain polyol, a chain-lengthening agent and an organic diisocyanate by a conventional method. At this time, as a method for introducing a sulfonium salt structure into the polyurethane resin, a dihydroxy compound having a sulfonium salt structure represented by the following general formula [Chemical Formula 2] is used as at least a part of the chain extender, or , A long-chain polyol containing the compound as part of its constituents.

[0007]

[Chemical 2] (In the formula, X and Y represent an alkylene group which may be the same as or different from each other, and R and R'represent an alkyl group and an aryl group which may be the same as or different from each other. Examples of the sulfonium salt compound represented by [Chemical Formula 2] include methyldi (2-hydroxyethyl) sulfoniumbenzenesulfonate, methyldi (2-hydroxyethyl) sulfoniumtoluenesulfonate, ethyldi (2-hydroxyethyl) sulfoniumbenzenesulfonate, ethyldi ( Examples thereof include 2-hydroxyethyl) sulfonium tosylate, methyldi (2-hydroxyethyl) sulfonium methanesulfonate, benzyldi (2-hydroxyethyl) sulfonium toluenesulfonate, etc. A sulfonium salt compound is a part of the constituent components. Examples of the long-chain polyol contained as a starting material include polyester polyols and polycarbonate polyols produced by using a dihydroxy compound having a sulfonium salt structure represented by the general formula [Chem. 2] as a diol component, and a dihydroxy compound having a sulfonium salt structure described above. Examples thereof include polycaprolactone polyols, ethylene oxide polymers, propylene oxide polymers, ethylene oxide / propylene oxide copolymers, etc. produced as agent components.

The polyurethane resin according to the present invention can also be produced by reacting a sulfide group-introduced polyurethane resin with a sulfonate ester. As a method of introducing a sulfide group into a polyurethane resin, for example, 2,2
′ -Thiodiethanol and polyester polyols and polycarbonate polyols produced using this,
It is carried out by a conventional method using polycaprolactone polyol, polyether polyol and the like. The sulfide group-introduced polyurethane resin thus obtained can be reacted with sulfonic acid esters to obtain a polyurethane resin having a sulfonium salt structure. Examples of sulfonates that can be used in the present invention include methyl benzene sulfonate, ethyl benzene sulfonate, methyl p-toluene sulfonate, ethyl p-toluene sulfonate,
Examples include methyl methanesulfonate and ethyl methanesulfonate. The content of the sulfonium salt in the polyurethane resin is preferably 0.01 mmol / g to 1.0 mmol / g.

Examples of the organic diisocyanate used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate and p-. Phenylene diisocyanate, 1,5-naphthalene diisocyanate, xylene diisocyanate, tetramethyl xylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 4,4′-methylene bis (cyclohexyl isocyanate) and the like can be mentioned. Used alone or in any combination. Examples of long-chain polyols include polyester polyols, polycaprolactone polyols, polycarbonate polyols, polyether polyols, and other known compounds that have been conventionally used for producing polyurethane resins, and these can be used alone or in any combination as a mixture. Or it is used as a copolymer. Examples of chain lengthening agents include ethylene glycol, propylene glycol, 1,3-butanediol,
1,4-butanediol, 1,5-pentanediol,
Neopentyl glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-bis (hydroxyethoxy) benzene, glycerin, trimethylolpropane, dimethylolpropion Examples thereof include acids, short-chain polyhydric alcohols such as sodium 3,5-bis (hydroxyethoxy) benzenesulfonate, amines such as ethylenediamine, hexamethylenediamine, isophoronediamine, and xylenediamine, and water. As a method for producing the polyurethane resin according to the present invention, a solution polymerization method is preferable, but a method of dissolving a solid substance obtained by bulk polymerization in an appropriate organic solvent is also effective.

The polyurethane resin according to the present invention can be used in any combination with other binder resins and in any ratio. For example, the ratio of the polyurethane resin of the present invention to another binder resin is 10:90 to.
It can be used together in a 90:10 weight ratio. The weight ratio is preferably 20:80 to 80:20. Examples of these binder resins include vinyl chloride resins, vinylidene chloride resins, vinyl chloride / vinyl acetate / vinyl alcohol copolymers, alkyd resins, epoxy resins, polyurethane resins, nitrocellulose resins, poly Butyral-based resins and the like are included. When using the polyurethane resin according to the present invention to prepare a dispersion liquid, auxiliary components other than the above, for example, a dispersant, an antistatic agent, a surfactant,
A lubricant, a cross-linking agent, etc. can be used as necessary.

Examples of the crosslinking agent that can be used in the present invention are:
Various polyisocyanate compounds, namely polymethylene polyphenylene polyisocyanate, trimer of tolylene diisocyanate, trimer of hexamethylene diisocyanate, biuret-modified tolylene diisocyanate,
Examples include biuret-modified hexamethylene diisocyanate, carbodimide-modified 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate and trimethylolpropane adduct, and hexamethylene diisocyanate and trimethylolpropane adduct, which may be used alone or in any combination. Can be used in. The proportion of the cross-linking agent used with respect to the binder resin is 1 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the binder resin in terms of solid content. As a method for preparing the dispersion liquid, a known method, that is, a ball mill, a sand mill or the like can be used.

[0012]

Since the polyurethane resin binder according to the present invention has a sulfonium salt structure, the magnetic recording medium obtained by using the binder has a surface smoothness superior to that of the conventional one. And electromagnetic conversion characteristics are shown.

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention.

EXAMPLE 1 Polybutylene adipate (molecular weight 989) 43.1000 was added to a 1000 ml four-necked flask equipped with a stirrer and a cooling tube.
5 g, polyhexamethylene iphthalate (molecular weight 100
9) 133.1 g, neopentyl glycol 4.6 g,
7.7 g of methyldi (2-hydroxyethyl) sulfoniumtoluenesulfonate and 250 g of cyclohexanone as a solvent were charged. Then, 4,4′-diphenylmethane diisocyanate 6 which had been previously heated and melted was added to this.
1.2 g was charged and reacted at 85 ° C. Since the viscosity increases with time, while diluting with cyclohexanone as a solvent at a suitable time, 2280 cm in the infrared absorption spectrum
^The reaction was terminated when the absorption of the isocyanate group of ^-1 disappeared, and a light yellow transparent viscous polyurethane resin solution having a solid content of 25% was obtained.

Example 2 Polybutylene adipate (molecular weight 989) 40.000 was added to a 1000 ml four-necked flask equipped with a stirrer and a cooling tube.
9 g, polyhexamethylene iphthalate (molecular weight 100
9) 125.2 g, neopentyl glycol 4.3 g,
15.4 g of methyldi (2-hydroxyethyl) sulfonium toluenesulfonate and 250 g of cyclohexanone as a solvent were charged. Then, 4,4′-diphenylmethane diisocyanate 6 which had been previously heated and melted was added to this.
4.2 g was charged and reacted at 85 ° C. Since the viscosity increases with time, while diluting with cyclohexanone as a solvent at a suitable time, 2280 cm in the infrared absorption spectrum
^The reaction was terminated when the absorption of the isocyanate group of ^-1 disappeared, and a light yellow transparent viscous polyurethane resin solution having a solid content of 25% was obtained.

Example 3 Polybutylene adipate (molecular weight 989) 43.1000 was added to a 1000 ml four-necked flask equipped with a stirrer and a cooling tube.
1 g, polyhexamethylene iphthalate (molecular weight 100
9) 132.0 g, neopentyl glycol 4.5 g,
9.6 g of benzyldi (2-hydroxyethyl) sulfonium toluenesulfonate and 250 g of cyclohexanone as a solvent were charged. Then, 4,4′-diphenylmethane diisocyanate 6 which had been previously heated and melted was added to this.
0.8 g was charged and reacted at 85 ° C. Since the viscosity increases with time, while diluting with cyclohexanone as a solvent at a suitable time, 2280 cm in the infrared absorption spectrum
^The reaction was terminated when the absorption of the isocyanate group of ^-1 disappeared, and a light yellow transparent viscous polyurethane resin solution having a solid content of 25% was obtained.

Example 4 A 1000 ml four-necked flask equipped with a stirrer and a cooling tube was charged with polybutylene adipate (molecular weight 989) 40.
2 g, polyhexamethylene iphthalate (molecular weight 100
9) 123.0 g, neopentyl glycol 4.2 g,
19.2 g of benzyldi (2-hydroxyethyl) sulfoniumtoluenesulfonate and 250 g of cyclohexanone as a solvent were charged. Next, 63.3 g of 4,4′-diphenylmethane diisocyanate that had been heated and melted was charged into this and reacted at 85 ° C. Since the viscosity increases with time, 2280c in the infrared absorption spectrum is obtained while diluting with cyclohexanone as a solvent at appropriate times.
The reaction was terminated when the absorption of the isocyanate group of m ⁻¹ disappeared, and a pale yellow transparent viscous polyurethane resin solution having a solid content of 25% was obtained.

COMPARATIVE EXAMPLE 1 Polybutylene adipate (molecular weight 989) 46.m was placed in a 1000 ml four-necked flask equipped with a stirrer and a cooling tube.
0 g, polyhexamethylene iphthalate (molecular weight 100
9) 140.9 g, neopentyl glycol 4.8 g,
Then, 250 g of cyclohexanone was charged as a solvent. Then, 58.2 g of 4,4′-diphenylmethane diisocyanate that had been heated and melted was charged into this, and 85
The reaction was carried out at ° C. Since the viscosity increases with time, the reaction is terminated when the absorption of the isocyanate group at 2280 cm ^-1 in the infrared absorption spectrum disappears while being diluted with cyclohexanone as a solvent at a suitable time, and a pale yellow transparent viscous polyurethane resin solution having a solid content of 25% is obtained. Got

[Performance Test] The polyurethane resin solutions obtained in Examples 1 to 4 and Comparative Example 1 were subjected to dispersion treatment for 5 hours using a sand mill based on the following formulation. Co-γ-Fe ₂ O ₃ 100 parts by weight Polyurethane resin solution (solid content 25% by weight) 100 parts by weight Methyl ethyl ketone 110 parts by weight Toluene 110 parts by weight The dispersion thus obtained is applied to a polyethylene terephthalate film having a thickness of 10 μm and dried. Then, a magnetic layer having a thickness of 5 μm was formed. The results are shown in Table 1. In order to investigate the surface smoothness of the film on which the above magnetic layer is formed, a digital variable angle gloss meter (UGV- manufactured by Suga Test Instruments Co., Ltd.)
5D) was used to measure the glossiness of the magnetic layer surface. The results are shown in Table 1.

Example 5 In the performance test of Example 1, after 5 hours from the dispersion treatment, a crosslinking agent (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added in an amount of 10 parts by weight based on 100 parts by weight of the binder resin. A magnetic layer was formed in the same manner except that the dispersion treatment was performed for 1 hour, and the performance test was performed. The results are shown in Table 1.

Example 6 A mixture of the polyurethane resin of Example 1 and a vinyl chloride / vinyl acetate / vinyl alcohol copolymer (Sekisui Chemical Co., Ltd .: Eslec A) (weight ratio in solid content 50:50) was used as a binder. The same performance test as in Example 1 was performed except that the above was performed. The results are shown in Table 1.

[Table 1]

Claims (3)

[Claims] 1. A magnetic recording comprising a polyurethane resin produced from a long-chain polyol, a chain-lengthening agent, and an organic diisocyanate, having a sulfonium salt structure represented by the following general formula [Chem. 1] in the molecule. Polyurethane resin binder for media. [Chemical 1] (In the formula, A and B each represent a urethane residue which may be the same as or different from each other, and R and R ′ each represent an alkyl group or an aryl group which may be the same as or different from each other. .) 2. A polyurethane resin produced from a long-chain polyol, a chain-lengthening agent, and an organic diisocyanate, which has a sulfonium salt structure in the molecule, a vinyl chloride resin, a vinylidene chloride resin, and a vinyl chloride resin.
A magnetic recording comprising one or more of vinyl acetate / vinyl alcohol copolymer, alkyd resin, epoxy resin, polyurethane resin, nitrocellulose resin, and polybutyral resin. Polyurethane resin binder for media. 3. A polyurethane resin-based binder for a magnetic recording medium, comprising the polyurethane resin-based binder for a magnetic recording medium according to claim 1 or 2 and a crosslinking agent.