JPS58153230A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility, wear resistance, etc. by using polyurethane resin having tertiary amino groups and a polyisocyanate compound as components of a binder for the magnetic layer. CONSTITUTION:A magnetic layer for magnetic recording is formed using a binder consisting of thermoplastic polyurethane resin having 10,000-50,000mol. wt. and tertiary amino groups represented by the formula in the molecular chain and low mol.wt. polyisocyanate having 150-7,000mol.wt. and >=2 isocyanate groups or further contg. other resin. The amount of the polyisocyanate is 3- 40pts.wt. per 100pts.wt. polyurethane resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly, a special thermoplastic polyurethane resin is used as a binder component that contributes to improving the dispersibility of magnetic powder and the abrasion resistance of a magnetic layer. and a specific low molecular weight polyisocyanate.

In recent years, with the expansion of uses for magnetic recording media such as audio tapes and home VTR tapes, the required performance has become diverse. Improving the productivity of recording media is also a major issue.

Specific examples of the former include high recording density for reproducing clear images and sounds, high speed, withstanding long-term running under harsh conditions such as high temperature and high humidity, and no magnetic powder falling off from the magnetic layer. There are many things that can be mentioned.

Further, as an example of the latter, productivity of magnetic paint can be improved by shortening the time required for dispersing magnetic powder in a binder.

In other words, it is important to maintain the characteristics and physical properties of the magnetic layer and to improve the productivity of the binder, and to produce magnetic paints and high-performance magnetic recording media that can uniformly disperse magnetic powder in a shorter time. High sensitivity, high SN ratio, high C
There is a need for a binder that can provide good electromagnetic properties such as N ratio, and in addition has excellent durability such as wear resistance.

Various studies have been conducted to satisfy these properties, and in order to impart good wear resistance to the magnetic layer and improve the durability of magnetic recording media, mainly thermoplastic polyurethane resins and polyester resins have been studied. Binder systems consisting of isocyanates have been proposed.

However, thermoplastic polyurethane resins have the disadvantage of poor dispersibility of magnetic powder compared to binder resins such as cellulose resins and vinyl chloride-vinyl acetate copolymers.

The present inventors have completed the present invention as a result of various studies on a method for improving the above-mentioned drawbacks without impairing the excellent properties of thermoplastic polyurethane resin systems.

That is, the present invention provides a magnetic recording medium in which a magnetic layer consisting of magnetic powder, a binder, and an additive is provided on a plastic film, in which the binder C is a thermoplastic polyurethane resin III containing a tertiary amino group as shown below. A), and incyanate group 211
The present invention provides a magnetic recording medium comprising a low molecular weight polyincyanate (B) having the above properties.

The present invention shows that by using a thermoplastic polyurethane resin containing tertiary amino groups in the molecule and a low molecular weight polyisocyanate, the dispersibility of magnetic powder can be improved and the dispersion time can be significantly shortened. Furthermore, the mechanical strength, abrasion resistance, etc. of the magnetic layer are further increased, and the durability of the magnetic recording medium is also improved.

The molecular weight of the thermotransferable polyurethane resin Ill (A) of the present invention is 10.000 to 50.000, particularly 15.000 to 50.000.
A value of 35,000 is desirable, and values outside these ranges are not preferred because the excellent performance required by the present invention cannot be obtained.

The terminal groups may be an isocyanate group or a hydroxyl group at both ends, an isocyanate group at one end, and a hydroxyl group at the other end, but hydroxyl at both ends is preferred.

The thermoplastic polyurethane resin containing a tertiary amino group in the molecular weight group used in the present invention includes an organic diisocyanate and a diol containing a tertiary amino group alone, and a combination of the diol and a tertiary amino group in the molecular weight group. It can be obtained from a mixture of linear diols that do not contain amino groups.

Examples of organic diisocyanates include hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, xylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate,
2. 4-) lylene diisocyanate, 2,6-lylene diisocyanate), 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-
Examples include phenylene diisocyanate, 1,5-naphthylene diisocyanate, and mixtures thereof. Among these, 4.4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, 2°4-to1
Preferred are run diisocyanate, 2,6-dolylene diisocyanate and mixtures thereof.

Examples of linear diols containing no tertiary amino groups include polyether polyols, polyester polyols, and low molecular weight glycols having a molecular weight of 500 to 6,000 and having terminal hydroxyl groups. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.

In addition, as polyester polyol, ethylene I
7col, 1, 2-7'ropylene glycol, 2.3
-butylene glycol, 1゜4-butylene glycol,
2.2-dimethyl-1,3-diol, diethylene glycol, 1,5-pentamethylene glycol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool, etc. Glycols alone or in combination with succinic acid, maleic acid, adipic acid, glutaric acid,
pimelic acid, speric acid, azelaic acid, sebacic acid,
Examples include dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, hexahydroterephthalic acid, and hexahydroterephthalic acid, and those obtained by polycondensation with these acid esters and acid parite.

Furthermore, examples include polycaprolactone diols obtained by ring-opening addition polymerization of lactones such as -monocaprolactone in the presence of the above-mentioned glycols.

As the low molecular weight glycol, the above-mentioned glycols used in the production of the above-mentioned polyesters can be used alone or in mixtures. Furthermore, bisphenol A
Examples include diols in which 2 to 4 moles of ethylene oxide, propylene oxide, butylene oxide, etc. are added to 1-hydroquinone.

Examples of diols containing a tertiary amino group in the molecule include R-NH2 (R; Cn+H2m+t n-1 to 20
Diols and diols obtained by adding 2 to 50 moles of ethylene oxide, propylene oxide, or butylene oxide to the primary amines shown in ).

These derivatives include, for example, N-methyljetanolamine, which is obtained by adding 2 moles of ethylene oxide to primary amines such as methylamine, ethylamine, inpropylamine, n-butylamine, and isobutylamine; - Ethylene oxide to N-alkyl diethanolamines such as ethylgetanolamine, N-isopropylgetanolamine, N-n-butylgetanolamine, N-isobutylgetanolamine, laurylamine, stearylamine, oleylamine, etc. 2-50
Examples include diols in which ethylene oxide, propylene oxide, etc. are further added to alkylamines such as polyoxyethylene laurylamine, polyoxyethylene stearylamine, and polyoxyethylene oleylamine.

Further examples include polyester diols obtained by polycondensing a mixture of the N-alkyl jetanolamine and the glycols with the dibasic acids and their acid esters and acid halides. Also included are polycaprolactone diols obtained by ring-opening addition polymerization of lactones such as ε-caprolactone in the presence of a mixture of the above N-alkylgetanolamine and the above glycols.

When producing the thermoplastic polyurethane resin used in the present invention, the OH/
The molar ratio of NCO is preferably 0.80 to 1.20/1.00, preferably 0.90 to 1.10/1.00.

If it deviates from these ranges, it is not preferable because the excellent performances required by the present invention cannot be obtained.

If necessary, catalysts and various stabilizers can be used. Catalysts include, for example, triethylamine, triethylene diamine, morpholine,
Nitrogen compounds such as N-methylmorpholine, potassium acetate,
Examples include metal salts such as zinc stearate, and organometallic compounds such as dibutyltin dilaurate and diptyltin oxide. By incorporating stabilizers against ultraviolet light such as substituted benzotriazoles and stabilizers against thermal oxidation such as phenol derivatives, the above-mentioned properties of the thermoplastic polyurethane resin (A>) can be significantly stabilized.

Furthermore, in producing the thermoplastic polyurethane resin (A), conventionally known methods can be used, and if desired, after sufficiently mixing the reactants in the presence of a catalyst,
A method in which the reaction mixture is poured onto a lithographic plate or flat surface and heated, and then crushed after cooling. A method in which the reaction mixture is injected into an extruder. Dimethylformamide, toluene, xylene, benzene, dioxane, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone. ,Ethyl acetate,
A conventional production method using a solution reaction method in which the reaction is carried out in a single or mixed organic solvent such as butyl acetate can be used.

In the present invention, the thermoplastic polyurethane resin (A)
It is necessary to finally use it by curing it with a suitable curing agent, and low molecular weight polyisocyanate is most suitable as the curing agent.

Examples of the low molecular weight polyisocyanate having two or more isocyanate groups used in the present invention include organic diisocyanates used in the production of the thermoplastic polyurethane resin, low molecular weight polyisocyanates having two or more isocyanate groups, and blocking of these reactive groups. Examples include blocked isocyanates.

As the low molecular weight polyisocyanate having two or more incyanate groups, those having a molecular weight of 150 to 7,000 are preferable, and Dainippon Ink & Chemicals products, such as Parnock D
-750. D-Fish, DN-(6), DN-950, Crisbon NX, CL-2, Sumitomo Bayer's Desmosier L1 Desmodule RF, Desmosier R1 Som, and equivalent products commercially available from each company can be used.

Furthermore, as the blocked isocyanate, for example, Dainippon Ink & Chemicals @ product Parnock D-500, D-
550, D-504, etc.

By adding 3 to 40 parts by weight of the low molecular weight polyisocyanate to 111,100 parts by weight of the thermoplastic polyurethane resin and curing it, the mechanical strength, abrasion resistance, heat resistance, moist heat resistance, and solvent resistance of the magnetic layer are improved. And the adhesion to the base material can be greatly improved.

In addition, the binder component may contain, if necessary, a thermoplastic polyurethane resin, a vinyl chloride-vinyl acetate copolymer, a cellulose resin, a polyvinyl butyral resin, which is commonly used as a binder component for magnetic recording media. By using commercially available products such as thermoplastic polyester resin, vinyl chloride-vinyl propionate copolymer, epoxy resin, and phenoxy #1III1, the dispersibility of magnetic powder can be improved.
It can also be used to improve the smoothness of the surface of the magnetic layer.

The magnetic powder used in the present invention is, for example, rF620aF
e20a powder 4 powder, Co-containing r-Fe20a powder, C
Various conventionally known magnetic powders can be used, including o-containing F6aO+ powder, Cr02 powder, and the like.

The plastin film used in the present invention may be any commonly used film such as polyester film.

Next, the present invention will be explained by examples, but these are merely embodiments and the present invention is not limited by the examples. [Example 1] Molecular weight 1 obtained from ethylene glycol and adipic acid After mixing 150 parts of polyester diol with a resting value of 74.8), 6.5 parts of N-ethyljetanolamine, and 0.01 part of dibutyltin dilaurate, 36.8 parts of 4.4'-diphenylmethane diisocyanate was added. did. Before mixing these components, the polyol and isocyanate were heated to 90°C and 40°C, respectively.

The isocyanate was added to the polyol mixture by mechanical mixing for approximately 1 minute to ensure intimate contact of the components.The reaction mixture was then poured onto a vat heated to 120°C for 1 hour and then heated for 100 minutes. The reaction was completed by standing at ℃ for 20 hours. The number average molecular weight (hereinafter referred to as molecular weight) of the obtained thermoplastic polyurethane resin.

Ger Pan1latlon Chro+aatsg
raphs (abbreviated as GPC, calculated based on known polystyrene molecular weight) was about 20,000.

[Execution W42] 200 parts of polytetrahydrofuran with a molecular weight of 2.000 and a hydroxyl value of 56.1, 39.9 parts of N-ethyljetanolamine, 0.02 part of diptyltin dilaurate, and 32 parts of 4,4'-diphenylmethane diisocyanate.
The molecular weight was 18.5% in the same manner as in Example 1. ■ Thermoplastic polyurethane resin made from grains was obtained.

[Example 3] Molecular weight 3 using N-methyljetanolamine as an initiator
．． 000 (hydroxyl value 37.4) polycaprolactone 300 parts, 1.4-butylene glycol 3.6 parts, diptyltin dilaure) 0.02 parts, 2. 4-) lylene diisocyanate)/2. 6-) Example 1 using 23.9 parts of lylene diisocyanate (80 parts, 720 parts mixture)
A thermoplastic polyurethane resin having a molecular weight of 22,000 was obtained in the same manner as above.

[Comparative Examples 1 to 3] Comparative Example 1 is the same as Example 1 except that 3.1 parts of ethylene glycol was used instead of N-ethyljetanolamine. 1
In Example 2, 2.7 parts of 1.4-butylene gellicol was used instead of N-ethyljetanolamine, and in Comparative Example 3, 2.2-dimethyl was used instead of N-methyljetanolamine in Example 3. -1,3-propanediol as initiator, molecular weight 3.000 C1jt, acid value 3
Example 1 using 300 parts of polycaprolactone of 7.4)
A thermoplastic polyurethane resin containing no tertiary amino groups in the molecule was obtained by a similar method.

The molecular weights are, in order, 21. ■Ika, 000 and 23.00
It was 0.

The thermoplastic polyurethane resins of Examples 1 to 3 and Comparative Examples 1 to 3 were used to evaluate the dispersibility of magnetic powder and to measure the abrasion resistance of the magnetic tape, which will be described below.

Dispersibility of magnetic powder Thermosnowable polyurethane trees obtained in Examples 1 to 3 or Comparative Examples 1 to 3
150 parts cyclohexanone
425 parts methyl ethyl ketone
425 parts r-Fe20a powder
300 parts of the above mixture was milled in a ball mill for 20 hours, 35 hours, and 50 hours, and the resulting magnetic paint was coated on a polyethylene terephthalate base film with a thickness of 10 μm so that the thickness after drying was 10 μm. The surface condition of the magnetic layer was observed under a magnifying glass (40 times magnification) and the dispersibility of the magnetic powder was evaluated. The results are shown in Table 1 on the next page.

Table 1 Evaluation of dispersibility of magnetic powder by mirror observation] ◎: Very good ○: Excellent Δ: Fair×:
Poor XX = Very poor Table 1 confirms that the thermoplastic polyurethane resin of the present invention exhibits excellent dispersibility in a shorter time.

Abrasion resistance of magnetic tape Thermoplastic polyurethane resin '6 obtained in Examples 1 to 3 or Comparative Examples 1 to 3 60 parts Vinylite VAGB Fallow (vinyl chloride-vinyl acetate copolymer manufactured by Union Carpite Co.) 40 parts cyclohexane No. 300
methyl ethyl ketone
300 parts 7Fe20@magnetic powder
12 parts Lubricant 7 parts After kneading the above mixture in a ball mill for 30 hours, 30 parts of Parnock D-750 (low molecular weight polyisocyanate manufactured by Nippon Ink Chemical Industry ■) was added and the mixture was further kneaded for 1 hour. The resulting magnetic paint was applied onto a polyethylene terephthalate base film with a thickness of 10 μm to a thickness of 1 μm after drying.
It was coated and dried to a thickness of 0μ, and cut into a predetermined width to produce a magnetic recording tape.

The abrasion resistance of the obtained magnetic recording tape was measured.

Abrasion resistance was measured by rubbing the magnetic surface of each tape with a rotating disk and measuring the amount of abrasion in its thickness.

The results are shown in Figure 1.

From FIG. 1, it was confirmed that the magnetic tapes using the thermoplastic polyurethane resins of Examples 1 to 3 exhibited superiority in durability performance.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the amount of wear of the magnetic recording tape and time for the magnetic recording tapes obtained using the binders of each example and comparative example.

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer consisting of magnetic powder, a binder, and an additive is provided on a plastic film, the binder component is present in the molecular chain\N-R(R:Cn+H2m+t n-1 ~20)
? A magnetic recording medium comprising 1 ull of a cram-replaceable polyurethane resin containing the shown tertiary amino group (A) and a low molecular weight polyisocyanate (B) having two or more scratches in the isocyanate group,