JPH0652564B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly, to a high-performance magnetic recording having its magnetic layer formed from a dispersion liquid of magnetic particles containing a specific dispersant. Regarding the medium.

(Prior Art) Conventionally, a magnetic recording medium used in audio equipment, computers and the like is obtained by forming a magnetic layer composed of magnetic particles and a binder resin on a non-magnetic support such as a polyester film.

The formation of such a magnetic layer is performed by applying a dispersion liquid in which magnetic particles are dispersed in a medium containing a binder resin to a support, and these magnetic particles cause strong aggregation in the medium. Therefore, a stable dispersion cannot be obtained as it is.

Therefore, conventionally, various dispersants have been proposed and used in order to improve the dispersion stability of magnetic particles.

(Problems to be Solved by the Invention) However, the conventional dispersants cannot overcome the strong cohesive force of the magnetic particles, and the magnetic particles once dispersed re-aggregate within a short time. There is a problem that it must be used immediately after preparation, and there are various drawbacks in terms of productivity of the magnetic recording medium.

Furthermore, even in this way, since the conventional dispersant is an organic compound having a small to medium molecular weight which is essentially different from the binder resin used, it migrates to the surface after the formation of the magnetic layer,
This causes various problems such as damage to the recording head.

Therefore, there is a strong demand for a dispersant that breaks down the strong cohesive force of the magnetic particles to provide a stable dispersion liquid and that is integrated with the binder resin after the formation of the magnetic layer and does not migrate to the surface of the magnetic layer. There is.

The present inventor has conducted intensive studies to solve the above-mentioned conventional drawbacks and meet the above-mentioned demands, and as a result, when a specific dispersant is used in the production of a magnetic recording medium, the above-mentioned conventional techniques are used. The present invention has been completed by finding that the drawbacks can be solved.

(Means for Solving Problems) That is, the present invention comprises a non-magnetic support and a magnetic layer provided on one surface of the support, the magnetic layer comprising magnetic particles,
A dispersion formed of a binder resin, a dispersant and a medium, wherein the dispersant is a reaction product of a silane coupling agent having a reactive organic functional group and an organic polyisocyanate. It is a magnetic recording medium.

Explaining the present invention in more detail, the dispersant used in the present invention and the first feature of the present invention is a reaction product of a silane coupling agent having a reactive organic functional group and an organic polyisocyanate.

The silane coupling agent having a reactive organic functional group used to obtain such a dispersant has a general formula X-R-Y.
It is a compound represented by (I).

X in the above general formula (I) is a group capable of reacting with an isocyanate group, for example, an amino group, an epoxy group, a hydroxyl group, a thiol group, a carboxyl group and the like, and particularly preferable ones are an amino group, an epoxy group and a thiol group. It is a base.

R in the general formula (I) is any divalent organic group, and preferable ones are an aliphatic group having 2 to 20 carbon atoms, an aromatic group and an aliphatic aromatic group. The group (1) is capable of having an oxygen atom, a nitrogen atom or a sulfur atom therein as a linking group. Further, Y in the general formula (I) is Si.
(R) m (R ′) n (R is H or a C ₁ -C ₄ alkyl group, R ′ is a C ₁ -C ₄ alkoxy group,
m is 1-2 and n is 2-3. ).

Some preferred examples of the compound represented by the general formula (I) are as follows.

The silane coupling agent having a reactive organic functional group as described above is an example of a preferable silane coupling agent in the present invention, the present invention is not limited to these examples, and the compounds of the above-mentioned examples and Other compounds represented by the general formula (I) are commercially available at present and are easily available from the market, and any of them can be used in the present invention.

The organic polyisocyanate used in the present invention and secondly characterizing the present invention is a compound having at least two isocyanate groups in an aliphatic or aromatic compound, and has been widely used as a raw material for synthesizing polyurethanes conventionally. Has been done. Any of these known organic polyisocyanates are useful in the present invention. Particularly preferable organic polyisocyanates are as follows.

Toluene-2,4-diisocyanate 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate , 2,4-diisocyanate-diphenyl ether, mesitylene diisocyanate, 4,4-methylenebis (phenyl isocyanate), durylylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4,4-diisocyanate dibenzyl, 1,4-Tetramethylene diisocyanate, 1,6-Tetramethylene diisocyanate, 1,10-Decamethylene diisocyanate, 1,4-Cyclohexylene diisocyanate, Xylylene diisocyanate DOO, 4,4-methylenebis (cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, further, adducts of these organic polyisocyanates with other compounds, for example, Furthermore, urethane prepolymers having two or more isocyanate groups at the ends thereof and the like.

The dispersant used in the present invention comprises a silane coupling agent having a reactive organic functional group as described above and an organic polyisocyanate as described above, wherein the reactive organic functional group and the isocyanate group are approximately 1: 1. The functional group ratio is about 0 to 100 ° C. in the presence or absence of an organic solvent and a catalyst,
Preferably, it can be easily obtained by reacting at a temperature of 20 to 50 ° C. for about 10 minutes to 3 hours.

The organic solvent that may be used in the production of such a dispersant may be any organic solvent that is inert to the respective reaction raw materials and products, and for example, preferable organic solvents include methyl ethyl ketone and methyl. -N-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, cyclohexane, tetrahydrofuran, dioxane, methanol, ethanol, isopropyl alcohol, butanol, methyl cellosolve , Butyl cellosolve, cellosolve acetate, dimethylformamide, dimethylsulfoxide, pentane, hexane, cyclohexane, heptane, octane, mineral spirits, petroleum ether, gasoline, benzene, toluene Xylene, chloroform, carbon tetrachloride, chlorobenzene, perchlorethylene, trichlorethylene, and the like.

The dispersant used in the present invention obtained as described above may be separated from the organic solvent when it is produced using an organic solvent, or may be used as a solution of the organic solvent as it is. The dispersant used in the present invention separated from the organic solvent is generally a white to brown liquid or solid, and is easily soluble in an organic solvent for dispersing various magnetic particles in the related art.

The dispersion used in the present invention as described above, according to various analyses, for example, infrared absorption spectrum, elemental analysis, molecular weight measurement, etc., shows that the isocyanate group of the organic polyisocyanate and the reactive organic functional group of the silane coupling agent. And were subjected to an addition reaction, and, for example, when the reactive organic functional group was an amino group, it was revealed to be a compound in which both were bonded by an —NHCONH— bond.

According to a detailed study by the present inventor, the dispersant used in the present invention is extremely easy and stable to disperse various magnetic particles in a liquid medium containing a binder resin. Moreover, even if it is stored for a long time, it gels,
Does not cause thickening or aggregation / separation of magnetic particles, and
Even when the obtained dispersion is applied to various supports and dried to form a magnetic layer, it does not bleed onto the surface of the coating film or lower the strength of the coating film like the conventional dispersion liquid. It was found that the electrical, chemical and physical properties of the coating film are not impaired.

The dispersion used in the present invention is the above-mentioned dispersant, magnetic particles,
Binder resin and liquid medium are essential components.

The magnetic particles used in the present invention include, for example, iron, chromium, nickel, cobalt or alloys or oxides thereof, and modified products thereof, specifically, for example, γ
-Fe ₂ O _3, ferrite, magnetite, CrO
_2, etc., cobalt-doped γ-Fe ₂ O ₃ , a cobalt-doped Fe ₂ O ₃ and Fe ₃ O ₄ beltride compound, and the like.

The magnetic particles as described above are merely examples, and various magnetic particles other than the above examples can naturally be used in the same manner in the present invention, and can be used alone or as a mixture.

In the present invention, what is used as the binder resin is various binder resins conventionally used for forming a magnetic layer, and any of these can be used, for example, vinyl chloride resin, vinylidene chloride. Resin, vinyl chloride / vinyl acetate / vinyl alcohol copolymer resin, alkyd resin, epoxy resin, acrylonitrile-butadiene resin, polyurethane resin, nitrocellulose resin, polybutyral resin, polyester resin, silicone resin Examples thereof include resins, melamine-based resins, urea-based resins, acrylic-based resins, polyamide-based resins, and the like, with polyurethane-based resins being particularly preferred. Any of these resins may be used alone or as a mixture, and may be a solution or dispersion in an organic solvent.

As the liquid medium used in the present invention, an organic solvent or a mixture thereof in the preparation of the above-mentioned dispersant is used.

The dispersion used in the present invention contains the above-mentioned components as essential components, and their use ratio is the same as in the conventional dispersion of magnetic particles. For example, if the total dispersion is 100 parts by weight, The magnetic particles occupying therein are about 10 to 50% by weight, and the dispersant is about 5 to 20% by weight of these magnetic particles.
Generally, the liquid medium is about 50 to 90% by weight, and the binder resin is about 5 to 20% by weight.

The dispersion used in the present invention, as long as these components are essential components, other auxiliary components other than the above, for example, pigments, extender pigments, plasticizers, antistatic agents, surfactants, lubricants, crosslinking agents, and aging. It may contain any additives such as an inhibitor, a stabilizer, a foaming agent, an antifoaming agent and the like.

The manufacturing method itself of the dispersion liquid used in the present invention consisting of the above-mentioned essential components and optional components may be any conventionally known method, generally, ball mill treatment, mixer while adding the essential components simultaneously or sequentially. A mixing / dispersing method such as a treatment, a roll mill treatment, a bead mill treatment, a gravel mill treatment, a sand mill treatment, and a high speed impeller treatment is suitable.

Such a dispersion method itself has different conditions depending on the type, size, and use of the magnetic particles to be dispersed, but generally, if the treatment is carried out at a temperature of room temperature to 100 ° C. for about 5 minutes to 20 hours. Good.

As the support to be used, any conventionally known support can be used, and for example, a polyester film having a thickness of 5 to 50 μm, a polypropylene film, a cellulose triacetate film, a cellulose diacetate film, a polycarbonate film or the like can be arbitrarily used. You can

The magnetic layer is formed by coating the coating solution as described above on at least one surface of the support as described above and drying it to a thickness of about 5 to 2
It can be formed by applying an arbitrary method so as to have a thickness of 0 μm and then drying. The coating method and the drying method may be conventionally known methods.

(Operation / Effect) Since the magnetic layer of the magnetic recording medium of the present invention obtained as described above is formed from the dispersion liquid containing the specific dispersant as described above, its productivity is good.

That is, the dispersion liquid of the magnetic particles used in the present invention, since the dispersant used has an inorganic silane group, the silane group has some action on the magnetic particles, and other parts of the dispersant. Since is a group having a high affinity for the medium, the stability of the dispersion is extremely high.

Further, since the magnetic layer of the magnetic recording medium of the present invention is formed from the dispersion liquid containing the dispersant as described above, after the formation of the magnetic layer, the dispersant contained in the magnetic layer is combined with the binder resin. Since it is integrated, the disadvantage that the dispersant bleeds over the surface of the magnetic layer over time and causes various problems as in the prior art is solved.

Next, the present invention will be described more specifically with reference to Reference Examples, Examples and Comparative Examples. In addition, "parts" or "%" in the text are based on weight.

Reference Example 1 (Production Example of Dispersant) Adduct of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate (TDI) (Coronate L, manufactured by Nippon Polyurethane, NCO% 12.5, solid content 75%) 8
While stirring well at room temperature for 75 parts, 663 parts of 3-aminopropyltriethoxysilane is gradually added dropwise to the reaction mixture.

After the completion of the reaction, the ethyl acetate was evaporated to obtain 1300 parts of a white solid dispersant.

According to the infrared absorption spectrum of this dispersant, 2270 /
The absorption by the free isocyanate group of cm disappeared, and the absorption band by the Si-O-C group was shown at 1090 / cm. Moreover, the measurement result of the molecular weight by the freezing point depression method is
The theoretical value was 1319, whereas the measured value was 1305, which was in good agreement with the theoretical value.

Therefore, the dispersant and the main structure are estimated to be the following formula.

Reference Example 2 (Production Example of Dispersant) Addition product of hexamethylene diisocyanate and water (Duranate 24A-100, Asahi Kasei, NCO% 23.5)
While well stirring 150 parts at room temperature, 186 parts of 3-aminopropyltriethoxysilane was gradually added dropwise to the mixture and reacted to obtain 330 parts of a colorless transparent liquid dispersant.

According to the infrared absorption spectrum of this dispersant, 2270 /
The absorption by the free isocyanate group of cm disappeared, and the absorption band by the Si-O-C group was shown at 1090 / cm.

Therefore, the main structure of the above dispersant is presumed to be the following formula.

Reference Example 3 (Production Example of Dispersant) 150 parts of an adduct (Takenate D110N, manufactured by Takeda Pharmaceutical Co., Ltd., NCO% 11.5, solid content 75%) of 1 mol of trimethylolpropane and 3 mol of xylylisocyanate is well maintained at room temperature While stirring, 81 parts of 3-mercaptopropyltrimethoxysilane was gradually dropped into this to react.

After the reaction was completed, ethyl acetate was evaporated to obtain 225 parts of a white solid dispersant.

According to the infrared absorption spectrum of this dispersant, 2270 /
The absorption by the free isocyanate group of cm disappeared, and the absorption band by the Si-O-C group was shown at 1090 / cm.

Therefore, the main structure of the above dispersant is presumed to be the following formula.

Reference Example 4 (Production Example of Dispersant) A mixture of 708 parts of 3-glycidoxypropyltrimethoxysilane and 387 parts of dibutylamine was reacted with 1 mol of trimethylolpropane and tolylenediisocyanate 3
The mixture is gradually added dropwise to 875 parts of an adduct with a mole (Coronate L) at room temperature with thorough stirring for reaction.

After completion of the reaction, the ethyl acetate was evaporated to obtain 1740 parts of a white solid dispersant.

According to the infrared absorption spectrum of this dispersant, 2270 /
The absorption by the free isocyanate group of cm disappeared, and the absorption band by the Si-O-C group was shown at 1090 / cm.

Therefore, the main structure of the above dispersant is presumed to be the following formula.

Reference Example 5 (Production Example of Dispersant) 442 parts of 3-aminopropyltriethoxysilane was dissolved in methyl ethyl ketone and stirred well at room temperature.
262 parts of 4,4'-methylenebis (cyclohexyl isocyanate) is gradually added dropwise to react.

After completion of the reaction, the ethyl acetate is evaporated to obtain a liquid dispersant 6
95 parts were obtained.

According to the infrared absorption spectrum of this dispersant, 2270 /
The absorption by the free isocyanate group of cm disappeared, and the absorption band by the Si-O-C group was shown at 1090 / cm. In addition, the measurement result of the molecular weight by the freezing point depression method was 704, whereas the theoretical value was 704, which was in good agreement with the theoretical value.

Therefore, the main structure of the above dispersant is presumed to be the following formula.

Reference Example 6 (Preparation of binder solution) 150 parts of polybutylene adipate having a hydroxyl group at the end and a molecular weight of 2000, 1,3-butylene glycol 20
And 52 parts of tolylene diisocyanate were subjected to an addition reaction in 412 parts of methyl ethyl ketone (solid content 35%) to obtain a polyurethane resin solution having a viscosity of 300 poises / 20 ° C.

Reference Example 7 (Preparation of Dispersion) r-Fe ₂ O ₃ 100 parts Dispersant of Reference Example 1 7 parts Binder solution of Reference Example 6 (35% solution) 85 parts Dispersant (lecithin) 2 parts Carbon black 2 parts Methyl ethyl ketone 67 parts Triol 67 parts Cyclohexanone 67 parts The above components were mixed and kneaded in a ball mill for 50 hours, 8 parts of Coronate L was further added, and kneading was further performed for 3 hours to obtain a dispersion (A) of magnetic particles through a filter. .

Reference Example 8 (Preparation of Dispersion Liquid) A dispersion liquid (B) of magnetic particles was obtained in the same manner as in Reference Example 7 except that the dispersant of Reference Example 2 was used instead of the dispersant of Reference Example 7.

Reference Example 9 (Preparation of Dispersion Liquid) A dispersion liquid (C) of magnetic particles was obtained in the same manner as in Reference Example 7 except that the dispersant of Reference Example 3 was used in place of the dispersant of Reference Example 7.

Reference Example 10 (Preparation of Dispersion Liquid) A dispersion liquid (D) of magnetic particles was obtained in the same manner as in Reference Example 7 except that the dispersant of Reference Example 4 was used in place of the dispersant of Reference Example 7.

Reference Example 11 (Preparation of Dispersion Liquid) A magnetic particle dispersion liquid (E) was obtained in the same manner as in Reference Example 7 except that the solution of Reference Example 5 was used instead of the dispersant of Reference Example 7.

Reference Example 13 (Preparation of Dispersion) Instead of the binder solution in Reference Example 7, a 35% methyl ethyl ketone solution of vinyl chloride / vinyl acetate / vinyl alcohol copolymer resin (Eslec A, Sekisui Chemical Co., Ltd.) was used, and the others were used. A dispersion (F) of magnetic particles was obtained in the same manner as in Reference Example 7.

Reference Example 13 (Preparation of Dispersion) Instead of the binder solution in Reference Example 7, a 35% methyl ethyl ketone solution of butyral resin (Eslec B, BL-2, manufactured by Sekisui Chemical Co., Ltd.) was used, and otherwise the same as in Reference Example 7. A dispersion (G) of magnetic particles was obtained.

Examples 1 to 7 Dispersions A to G obtained in Reference Examples 7 to 13 were applied on a polyester film by a reverse roll coater to a thickness of 20 μm and dried at room temperature for 2 hours, Seven kinds of magnetic recording media of the present invention were obtained by drying in an oven at 80 ° C. for 24 hours.

Comparative Example 1 Except that the dispersant of the present invention was not used,
A dispersion was prepared in the same manner as in Reference Example 7, and a magnetic recording medium for comparison was obtained in the same manner as in Examples 1 to 7 using the dispersion.

Comparative Example 2 In Reference Example 7, a dispersion liquid was prepared by using 7 parts of 3-aminopropyltriethoxysilane instead of the dispersant which characterizes the present invention, and the dispersion liquid was used to prepare Examples 1 to 7. Similarly, a magnetic recording medium for comparison was obtained.

Comparative Example 3 In Reference Example 7, a dispersion liquid was prepared by using 7 parts of 3-glycidoxypropyltriethoxysilane in place of the dispersant characterizing the present invention, and the dispersion liquid was used to prepare Example 1
A magnetic recording medium for comparison was obtained in the same manner as described above.

Performance Evaluation When the surface gloss of the magnetic layers of the magnetic recording media of Examples 1 to 7 and Comparative Examples 1 to 3 was examined according to JIS Z8741, the following results were obtained. As is clear from the table below, it was found that the magnetic recording medium of the present invention had excellent surface gloss and that the magnetic particles were dispersed uniformly without agglomeration. When the surface smoothness and the bleeding of the dispersant on the surface were examined, no bleeding was observed in the case of the present invention.

Continuation of the front page (56) References JP-A-56-143533 (JP, A) JP-A-51-131303 (JP, A)

Claims (2)

[Claims] 1. A non-magnetic support and a magnetic layer provided on one surface of the support, the magnetic layer being formed from a dispersion liquid containing magnetic particles, a binder resin, a dispersant and a medium. The magnetic recording medium, wherein the dispersant is a reaction product of a silane coupling agent having a reactive organic functional group and an organic polyisocyanate. 2. The magnetic recording medium according to claim 1, wherein the binder resin is a polyurethane resin.